wctype: Rely on module iswpunct. * m4/wctype.m4 (gl_FUNC_WCTYPE): Also test whether the "punct" class works. * modules/wctype (Depends-on): Add iswpunct. * tests/test-iswctype.c (main): Add more tests of the "punct" class. * doc/posix-functions/wctype.texi: Mention the Android problem.