Downgrade 'attribute ignored when parsing type' from error to warning, to match
the diagnostic's warn_ name. Switch some places (notably C++11 attributes)
which really wanted an error over to a different diagnostic. Finally, suppress
the diagnostic entirely for __ptr32, __ptr64 and __w64, to avoid producing
diagnostics in important system headers.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173788 91177308-0d34-0410-b5e6-96231b3b80d8