This commit alphabetizes all includes in libcxx. This is a NFC.
This can also serve as a pseudo "announcement" for how we should order these headers going forward (note: double underscores go before other headers).
Differential Revision: https://reviews.llvm.org/D102941
Including xlocinfo.h is a bit of a layering violation; locale.h is
the C library header we should use, while xlocinfo.h is essentially
part of the MS C++ library. Including xlocinfo.h brings in yvals.h,
which brings in yvals_core.h, which defines the MS STL's version
support macros, overriding what libc++'s <version> had defined.
Instead just include locale.h, and provide the few defines we need
for locale categories manually.
Differential Revision: https://reviews.llvm.org/D99213
We do ship those headers, so the directory name should not be something
that can potentially conflict with user-defined directories.
Differential Revision: https://reviews.llvm.org/D95956