[libcxx] [test] Change comments to say C++ instead of c++. NFC.

This makes them consistent (many comments already used uppercase).

The special REQUIRES, UNSUPPORTED, and XFAIL comments are excluded from this change.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@309468 91177308-0d34-0410-b5e6-96231b3b80d8
34 files changed