Import wchar and wctype-h explicitly

Import wchar and wctype-h explicitly

gnulib module wchar and wctype-h was imported as a dependency, but
they are used by gdb_wchar.h too.  This patch is to import them
explicitly.

gdb:

	* gnulib/update-gnulib.sh (IMPORTED_GNULIB_MODULES): Add wchar
	and wctype-h.
	* gnulib/import/Makefile.am: Re-generated.
	* gnulib/import/Makefile.in: Likewise.
	* gnulib/import/m4/gnulib-cache.m4: Likewise.