Summary:
Because `locale.h` isn't part of the libc++ modules the class definitions it provides are exported as part of `__locale` (since it happens to be build first). This breaks `<clocale>` which exports `std::lconv` without including `<__locale>`.
This patch implements `locale.h` to fix this issue, it also adds support for testing libc++ with modules.
Reviewers: mclow.lists, rsmith, EricWF
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D26826
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@287413 91177308-0d34-0410-b5e6-96231b3b80d8
