Suppress -Wshadow / -Wold-style-cast expanded from system header macros

Thanks to Jonathan Sauer for providing initial test cases.

Fixes PR16093 and PR18147.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197150 91177308-0d34-0410-b5e6-96231b3b80d8