Errors while compiling 25.2rc2

[Fabrice Popineau <fabrice.popineau@gmail.com>]

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I get errors when trying to compile the emacs-25 git branch on
Windows Subsystem for Linux, which is basically Ubuntu 16.04.

I get a bunch of errors like this :

  CC       careadlinkat.o
In file included from ../../emacs/src/conf_post.h:241:0,
                 from ../src/config.h:1917,
                 from ../../emacs/lib/careadlinkat.c:21:
./unistd.h: In function ‘rpl_pipe2’:
./unistd.h:1409:1: error: expected declaration specifiers before
‘_GL_ARG_NONNULL’
 _GL_FUNCDECL_RPL (pipe2, int, (int fd[2], int flags) _GL_ARG_NONNULL
((1)));
 ^
./unistd.h:1410:1: error: storage class specified for parameter
‘_gl_cxxalias_dummy’
 _GL_CXXALIAS_RPL (pipe2, int, (int fd[2], int flags));
 ^
./unistd.h:1415:1: error: storage class specified for parameter
‘_gl_cxxalias_dummy’
 _GL_CXXALIASWARN (pipe2);
 ^
./unistd.h:1415:1: error: redefinition of parameter ‘_gl_cxxalias_dummy’
./unistd.h:1410:1: note: previous definition of ‘_gl_cxxalias_dummy’ was
here
 _GL_CXXALIAS_RPL (pipe2, int, (int fd[2], int flags));
 ^
./unistd.h:1538:1: error: storage class specified for parameter
‘_gl_cxxalias_dummy’
 _GL_CXXALIAS_SYS (readlink, ssize_t,
 ^
./unistd.h:1538:1: error: redefinition of parameter ‘_gl_cxxalias_dummy’
./unistd.h:1415:1: note: previous definition of ‘_gl_cxxalias_dummy’ was
here
 _GL_CXXALIASWARN (pipe2);
 ^
./unistd.h:1541:1: error: storage class specified for parameter
‘_gl_cxxalias_dummy’
 _GL_CXXALIASWARN (readlink);
 ^
GCC version :

fabrice@LOBSANG:/mnt/d/Source/emacs/build-emacs-ubuntu$ gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


What could cause these problems ?

I know the platform may not be the primary target to support but still I'd
like to know what is happening there.

Thanks for any clue,

Fabrice

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