New module 'wcscpy'.

New module 'wcscpy'.

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