I think it should look like this:

--- cdefs.h 2017-12-04 13:27:55.640000000 +0100
+++ cdefs.new.h 2017-12-04 13:31:53.820000000 +0100
@@ -1,4 +1,4 @@
-/* Copyright (C) 1992-2017 Free Software Foundation, Inc.
+y/* Copyright (C) 1992-2017 Free Software Foundation, Inc.
    This file is part of the GNU C Library.

    The GNU C Library is free software; you can redistribute it and/or
@@ -471,10 +471,10 @@
    testing __STDC_VERSION__ for generic selection support.
    On the other hand, Clang also defines __GNUC__, so a clang-specific
    check is required to enable the use of generic selection.  */
-#if __GNUC_PREREQ (4, 9) \
+#if !defined __cplusplus && (__GNUC_PREREQ (4, 9)   \
     || __glibc_clang_has_extension (c_generic_selections) \
     || (!defined __GNUC__ && defined __STDC_VERSION__ \
- && __STDC_VERSION__ >= 201112L)
+ && __STDC_VERSION__ >= 201112L))
 # define __HAVE_GENERIC_SELECTION 1
 #else
 # define __HAVE_GENERIC_SELECTION 0


2017-12-04 13:21 GMT+01:00 Gábor Boskovits <boskovits@gmail.com>:

> We also have this in bits/floatn.h, but this seems right.
>
> #if (defined __x86_64__                                                 \
>      ? __GNUC_PREREQ (4, 3)                                             \
>      : (defined __GNU__ ? __GNUC_PREREQ (4, 5) : __GNUC_PREREQ (4, 4)))
> # define __HAVE_FLOAT128 1
> #else
> # define __HAVE_FLOAT128 0
> #endif
>
> /* Defined to 1 if __HAVE_FLOAT128 is 1 and the type is ABI-distinct
>
>
>    from the default float, double and long double types in this glibc.  */
> #if __HAVE_FLOAT128
> # define __HAVE_DISTINCT_FLOAT128 1
> #else
> # define __HAVE_DISTINCT_FLOAT128 0
> #endif
>
> I think the problem is caused by HAVE_GENERIC_SELECTION defined when we
> are in C++.
>
>
> 2017-12-04 13:18 GMT+01:00 Gábor Boskovits <boskovits@gmail.com>:
>
>> We have this in cdefs.h:
>> #if __GNUC_PREREQ (4, 9) \
>>     || __glibc_clang_has_extension (c_generic_selections) \
>>     || (!defined __GNUC__ && defined __STDC_VERSION__ \
>>         && __STDC_VERSION__ >= 201112L)
>> # define __HAVE_GENERIC_SELECTION 1
>> #else
>> # define __HAVE_GENERIC_SELECTION 0
>> #endif
>>
>> This does not seem right.
>>
>> We should not have this defined when compiling c++.
>> WDYT?
>>
>> 2017-12-04 13:03 GMT+01:00 Gábor Boskovits <boskovits@gmail.com>:
>>
>>> This minimal file reproduces the problem in icu4c 60.1 in guix
>>> environment icu4c on current core-updates.
>>>
>>> #include <cmath>
>>>
>>> int main(int argc, char **argv)
>>> {
>>>   std::signbit(1);
>>>   return 0;
>>> }
>>>
>>> It seems, that it is some problem with cmath.h
>>>
>>> /gnu/store/2wzijwwgpcdb1msmn3wgq9zmrbrkpx2h-gcc-5.5.0/includ
>>> e/c++/cmath:44:0
>>>
>>> The definition is in glibc 2.26 math.h, looks like this:
>>>
>>> #elif __HAVE_DISTINCT_FLOAT128
>>> # if __HAVE_GENERIC_SELECTION
>>> #  define __MATH_TG(TG_ARG, FUNC, ARGS)         \
>>>      _Generic ((TG_ARG),                        \
>>>        float: FUNC ## f ARGS,           \
>>>                default: FUNC ARGS,              \
>>>                long double: FUNC ## l ARGS,     \
>>>                _Float128: FUNC ## f128 ARGS)
>>>
>>>
>>>
>>> 2017-12-03 23:25 GMT+01:00 Gábor Boskovits <boskovits@gmail.com>:
>>>
>>>> It seems, that the fix is already included in the 60.1 release for the
>>>> xlocal problem. I think we can ignore that.
>>>>
>>>> 2017-12-03 23:20 GMT+01:00 Gábor Boskovits <boskovits@gmail.com>:
>>>>
>>>>> It seems, that they issued that already:
>>>>> http://bugs.icu-project.org/trac/changeset/40603
>>>>>
>>>>> 2017-12-03 23:08 GMT+01:00 Gábor Boskovits <boskovits@gmail.com>:
>>>>>
>>>>>> Ok, I found this one:
>>>>>> https://sourceware.org/glibc/wiki/Release/2.26#Removal_of_.2
>>>>>> 7xlocale.h.27
>>>>>>
>>>>>> It seems, that xlocale.h should not be used as an include, and glibc
>>>>>> removed that.
>>>>>>
>>>>>> So this is ok.
>>>>>>
>>>>>> The question is if this issue was addressed by icu4c, so we can just
>>>>>> go to the next step, or should we do something about this.
>>>>>>
>>>>>>
>>>>>> 2017-12-03 23:04 GMT+01:00 Gábor Boskovits <boskovits@gmail.com>:
>>>>>>
>>>>>>> I've found that simply reverting the update to icu4c 60 commit
>>>>>>> brings up the issue you just mentioned, with missing xlocale.h.
>>>>>>> So it seems, that the one you found introduced the xlocale problem,
>>>>>>> while 4e080fbb0bb73e4444181599676f4e1ef5fdc2ba introduces the new
>>>>>>> error.
>>>>>>> I think we should deal with the one you find first, the see what's
>>>>>>> with this newer one.
>>>>>>>
>>>>>>> We also have a long running discussion on a bug introduced by a
>>>>>>> later glibc update, ee3ebf1a357bd4eb36a2fa1790a7b549cffb305a which
>>>>>>> broke a lot of packages. Might these be somehow related?
>>>>>>> https://debbugs.gnu.org/cgi/bugreport.cgi?bug=29537
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> 2017-12-03 22:46 GMT+01:00 Chris Marusich <cmmarusich@gmail.com>:
>>>>>>>
>>>>>>>> Gábor Boskovits <boskovits@gmail.com> writes:
>>>>>>>>
>>>>>>>> > Any news on this icu4c thing?
>>>>>>>>
>>>>>>>> After about 2 days of running git bisect, my computer has informed
>>>>>>>> me
>>>>>>>> that the first bad commit is 67d527e35e367c9e9e89ec01cda2ce
>>>>>>>> 32cabd2d89.
>>>>>>>> This is the first commit where icu4c fails to build on core-updates.
>>>>>>>> The build failure at this commit is as follows:
>>>>>>>>
>>>>>>>> --8<---------------cut here---------------start------------->8---
>>>>>>>>    g++   ...  decimfmt.cpp
>>>>>>>>    g++   ...  decimalformatpattern.cpp
>>>>>>>>    g++   ...  dcfmtsym.cpp
>>>>>>>>    g++   ...  digitlst.cpp
>>>>>>>>    g++   ...  fmtable_cnv.cpp
>>>>>>>> digitlst.cpp:67:24: fatal error: xlocale.h: No such file or
>>>>>>>> directory
>>>>>>>> compilation terminated.
>>>>>>>> *** Failed compilation command follows:
>>>>>>>> ----------------------------------------------------------
>>>>>>>> g++ -D_REENTRANT -DU_HAVE_ELF_H=1 -DU_HAVE_ATOMIC=1
>>>>>>>> -DU_HAVE_STRTOD_L=1 -I. -I../common -DU_ATTRIBUTE_DEPRECATED=
>>>>>>>> -DU_I18N_IMPLEMENTATION -O2 -W -Wall -pedantic -Wpointer-arith
>>>>>>>> -Wwrite-strings -Wno-long-long --std=c++0x -c -DPIC -fPIC -o digitlst.o
>>>>>>>> digitlst.cpp
>>>>>>>> --- ( rebuild with "make VERBOSE=1 all" to show all parameters )
>>>>>>>> --------
>>>>>>>> make[1]: *** [../config/mh-linux:51: digitlst.o] Error 1
>>>>>>>> make[1]: *** Waiting for unfinished jobs....
>>>>>>>> make[1]: Leaving directory '/tmp/guix-build-icu4c-58.2.dr
>>>>>>>> v-0/icu/source/i18n'
>>>>>>>> make: *** [Makefile:143: all-recursive] Error 2
>>>>>>>> phase `build' failed after 59.0 seconds
>>>>>>>> builder for `/gnu/store/mdd6glhc0dg65y4wd11y0b7sbky9cwv6-icu4c-58.2.drv'
>>>>>>>> failed with exit code 1
>>>>>>>> @ build-failed /gnu/store/mdd6glhc0dg65y4wd11y0b7sbky9cwv6-icu4c-58.2.drv
>>>>>>>> - 1 builder for `/gnu/store/mdd6glhc0dg65y4wd11y0b7sbky9cwv6-icu4c-58.2.drv'
>>>>>>>> failed with exit code 1
>>>>>>>> guix build: error: build failed: build of
>>>>>>>> `/gnu/store/mdd6glhc0dg65y4wd11y0b7sbky9cwv6-icu4c-58.2.drv' failed
>>>>>>>> --8<---------------cut here---------------end--------------->8---
>>>>>>>>
>>>>>>>> Note that this is NOT the same error as the one that occurs at
>>>>>>>> commit
>>>>>>>> d6adba786cf2ab1b26ff083928b64262281ff106 (which is the commit on
>>>>>>>> core-updates from which Gábor's branch change-default-icedtea-8
>>>>>>>> branch
>>>>>>>> begins).  That error is:
>>>>>>>>
>>>>>>>> --8<---------------cut here---------------start------------->8---
>>>>>>>>    g++   ...  number_decimalquantity.cpp
>>>>>>>>    g++   ...  number_decimfmtprops.cpp
>>>>>>>> number_decimalquantity.cpp: In member function
>>>>>>>> ‘icu_60::number::impl::DecimalQuantity&
>>>>>>>> icu_60::number::impl::DecimalQuantity::setToDouble(double)’:
>>>>>>>> number_decimalquantity.cpp:333:9: error: ‘_Generic’ is not a
>>>>>>>> member of ‘std’
>>>>>>>>      if (std::signbit(n) != 0) {
>>>>>>>>          ^
>>>>>>>> In file included from /gnu/store/nz2m4gdvgzcrkqa4xwv
>>>>>>>> 360iskh7syj7i-gcc-5.5.0/include/c++/cmath:44:0,
>>>>>>>>                  from number_decimalquantity.cpp:9:
>>>>>>>> number_decimalquantity.cpp:333:14: error: expected
>>>>>>>> primary-expression before ‘float’
>>>>>>>>      if (std::signbit(n) != 0) {
>>>>>>>>               ^
>>>>>>>> number_decimalquantity.cpp:333:14: error: expected
>>>>>>>> primary-expression before ‘default’
>>>>>>>>      if (std::signbit(n) != 0) {
>>>>>>>>               ^
>>>>>>>> number_decimalquantity.cpp:333:14: error: expected
>>>>>>>> primary-expression before ‘long’
>>>>>>>>      if (std::signbit(n) != 0) {
>>>>>>>>               ^
>>>>>>>> number_decimalquantity.cpp:333:14: error: expected
>>>>>>>> primary-expression before ‘:’ token
>>>>>>>>      if (std::signbit(n) != 0) {
>>>>>>>>               ^
>>>>>>>> number_decimalquantity.cpp:337:9: error: ‘__builtin_isnan’ is not
>>>>>>>> a member of ‘std’
>>>>>>>>      if (std::isnan(n) != 0) {
>>>>>>>>          ^
>>>>>>>> number_decimalquantity.cpp:337:9: note: suggested alternative:
>>>>>>>> <built-in>: note:   ‘__builtin_isnan’
>>>>>>>> number_decimalquantity.cpp:339:16: error: ‘__builtin_isfinite’ is
>>>>>>>> not a member of ‘std’
>>>>>>>>      } else if (std::isfinite(n) == 0) {
>>>>>>>>                 ^
>>>>>>>> number_decimalquantity.cpp:339:16: note: suggested alternative:
>>>>>>>> <built-in>: note:   ‘__builtin_isfinite’
>>>>>>>> *** Failed compilation command follows:
>>>>>>>> ----------------------------------------------------------
>>>>>>>> g++ -D_REENTRANT -DU_HAVE_ELF_H=1 -DU_HAVE_ATOMIC=1
>>>>>>>> -DU_HAVE_STRTOD_L=1 -DU_HAVE_XLOCALE_H=0 -I. -I../common
>>>>>>>> -DU_ATTRIBUTE_DEPRECATED= -DU_I18N_IMPLEMENTATION -O2 -W -Wall -pedantic
>>>>>>>> -Wpointer-arith -Wwrite-strings -Wno-long-long -std=c++11 -c -DPIC -fPIC -o
>>>>>>>> number_decimalquantity.o number_decimalquantity.cpp
>>>>>>>> --- ( rebuild with "make VERBOSE=1 all" to show all parameters )
>>>>>>>> --------
>>>>>>>> make[1]: *** [../config/mh-linux:51: number_decimalquantity.o]
>>>>>>>> Error 1
>>>>>>>> make[1]: *** Waiting for unfinished jobs....
>>>>>>>> make[1]: Leaving directory '/tmp/guix-build-icu4c-60.1.dr
>>>>>>>> v-0/icu/source/i18n'
>>>>>>>> make: *** [Makefile:149: all-recursive] Error 2
>>>>>>>> phase `build' failed after 122.2 seconds
>>>>>>>> builder for `/gnu/store/8s6q5cll4knh7y0wfrbjqs2dai0x4sm2-icu4c-60.1.drv'
>>>>>>>> failed with exit code 1
>>>>>>>> @ build-failed /gnu/store/8s6q5cll4knh7y0wfrbjqs2dai0x4sm2-icu4c-60.1.drv
>>>>>>>> - 1 builder for `/gnu/store/8s6q5cll4knh7y0wfrbjqs2dai0x4sm2-icu4c-60.1.drv'
>>>>>>>> failed with exit code 1
>>>>>>>> guix build: error: build failed: build of
>>>>>>>> `/gnu/store/8s6q5cll4knh7y0wfrbjqs2dai0x4sm2-icu4c-60.1.drv' failed
>>>>>>>> --8<---------------cut here---------------end--------------->8---
>>>>>>>>
>>>>>>>> The fact that these errors are different suggests that more than one
>>>>>>>> problem may have been introduced...
>>>>>>>>
>>>>>>>> I haven't tried any more recent commits on core-updates.  I am not
>>>>>>>> sure
>>>>>>>> what the best way is to debug this, so I would appreciate any advice
>>>>>>>> anyone has.
>>>>>>>>
>>>>>>>> I hope that information helps.  Hopefully, together, we can untangle
>>>>>>>> this!
>>>>>>>>
>>>>>>>> --
>>>>>>>> Chris
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>