[BZ #18206]
* wcsmbs/wcsncmp.c (wcsncmp): Compare as wchar_t, not wint_t.
Use signed comparision instead of substraction to avoid
overflow bug.
* localedata/tests-mbwc/tst_wcsncmp.c (tst_wcsncmp):
Take the sign of ret.
* localedata/tests-mbwc/dat_wcsncmp.c (tst_wcsncmp_loc):
Do not expect precise return values. Only the sign matters.
* wcsmbs/Makefile (strop-tests): Add wcsncmp.
* wcsmbs/test-wcsncmp.c: New File.
* string/test-strncmp.c: Add wcsncmp support.
