It is intended to disable _all_ warnings, even those upgraded to
errors via `-Werror=warningname` or `#pragma clang diagnostic error'
Fixes: https://llvm.org/PR38231
Differential Revision: https://reviews.llvm.org/D53199
llvm-svn: 352535
the command line options (at least according to GCC's documentation). GCC 4.2
didn't appear to actually do this, but it seems like that has been fixed in
later release, so we will follow the docs.
llvm-svn: 141119