wcrtomb: Add more tests. * tests/test-wcrtomb-w32.c: Include localcharset.h. (test_one_locale): For the GB18030 and UTF-8 tests, verify that locale_charset() returns the expected value; otherwise, skip the test. * tests/test-wcrtomb-w32-6.sh: Remove old comment. * tests/test-wcrtomb-w32-7.sh: Likewise. * modules/wcrtomb-tests (Files): Add these files. (Depends-on): Add localcharset. (TESTS): Add test-wcrtomb-w32-6.sh, test-wcrtomb-w32-7.sh.