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/include/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 67d527e35e367c9e9e89ec01cda2ce32cabd2d89.
>>>>> 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::DecimalQ
>>>>> uantity::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
>>>>>
>>>>
>>>>
>>>
>>
>