clang-cl's system header detection doesn't kick in if we're using full
paths to the STL headers we need to include. And if certain headers
aren't recognized as system headers, we get a pile of warnings from
said headers. Use #include_next to ensure that system headers are
recognized as such, and suppress the warnings.
MozReview-Commit-ID: 4ZlAAGa49M1
--HG--
extra : rebase_source : c56711e09118fe930f389cc48543a661c293d7e4