Add an opt-in -Wheader-hygiene, which current diagnoses the use of
global using directives in C++ headers, from Elliot Glaysher!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@127881 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed