Other missing locales cause the relevant tests to be 'UNSUPPORTED' instead of failing. The failures that occurred for me are fixed in r258403 and a few additional ones are fixed in D16408.
Also, even with all the missing locales available there are two tests that fail when LANG=C is in the environment: libc++ :: std/localization/locale.categories/category.ctype/locale.ctype.byname/types.pass.cpp libc++ :: std/localization/locales/locale/locale.cons/char_pointer.pass.cpp I don't recall why I have that so I'm trying a build without it.
Merged in r258887 and r259058