New module 'wmemmove'.

New module 'wmemmove'.

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