Fix mbrtowc so that it never returns -1 in the C locale,
as this conflicts with a future version of POSIX
http://austingroupbugs.net/view.php?id=663#c2738
and causes problems with GNU grep: http://bugs.gnu.org/23234
See glibc bug 19932:
https://sourceware.org/bugzilla/show_bug.cgi?id=19932
* doc/posix-functions/mbrlen.texi (mbrlen):
* doc/posix-functions/mbrtowc.texi (mbrtowc):
Document the glibc bug.
* lib/mbrtowc.c [C_LOCALE_MAYBE_EILSEQ]:
Include hard-locale.h, locale.h.
(rpl_mbrtowc): Work around the C_LOCALE_MAYBE_EILSEQ bug,
if the bug is possible.
* m4/mbrtowc.m4 (gl_MBRTOWC_C_LOCALE): New macro.
(gl_FUNC_MBRTOWC): Use it, and define C_LOCALE_MAYBE_EILSEQ as needed.
* modules/hard-locale (License): Now LGPLv2+, for mbrtowc.
* modules/mbrtowc (Depends-on): Add hard-locale.
* modules/mbrtowc-tests (Files, TESTS): Add tests/test-mbrtowc5.sh.
* tests/test-mbrtowc.c (main): Test for bug fix if arg is '5'.
* tests/test-mbrtowc5.sh: New file.
