* modules/wmemchr: New file.
* lib/wchar.in.h (wmemchr): New declaration.
* lib/wmemchr.c: New file.
* lib/wmemchr-impl.h: New file, from libutf8 with modifications.
* m4/wmemchr.m4: New file.
* m4/wchar_h.m4 (gl_WCHAR_H_DEFAULTS): Initialize GNULIB_WMEMCHR,
HAVE_WMEMCHR.
* modules/wchar (Makefile.am): Substitute GNULIB_WMEMCHR, HAVE_WMEMCHR.
* tests/test-wchar-c++.cc: Test the declaration of wmemchr.
* doc/posix-functions/wmemchr.texi: Mention the new module.