Emacs build fails on Windows mingw64

[Andy Moreton]

Hi,

Arash Esbati reported on the emacs developer list that the build is
failing on Windows 10 with the MSYS2 toolchain:

https://lists.gnu.org/archive/html/emacs-devel/2021-10/msg01616.html

I can reproduce this problem on the emacs-28 and master branches of emacs.
The issue is with this hunk from gnulib string.in.h L456 (which matches
the gnulib master branch):

  # if __GNUC__ >= 11 && !defined strdup
  /* For -Wmismatched-dealloc: Associate strdup with free or rpl_free.  */
  _GL_FUNCDECL_SYS (strdup, char *,
                    (char const *__s)
                    _GL_ARG_NONNULL ((1))
                    _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC_FREE);
  # endif

_GL_ATTRIBUTE_MALLOC is not defined when this code is reached. This has
only appeared since a recent upgrade to gcc 11.2 in MSYS (previously my
machine had gcc 10.3).

Can this issue be addressed in gnulib so the emacs bug can be fixed ?

Thanks,

    AndyM