[libcxx] Additional 'REQUIRE' directives for tests that require en_US.UTF-8.

Summary:
These are the tests that didn't fail in the release candidate because they were
covered by another 'REQUIRES' directive.

Reviewers: mclow.lists, hans, bcraig, EricWF

Subscribers: EricWF, dim, cfe-commits

Differential Revision: http://reviews.llvm.org/D16408

llvm-svn: 258920