Revert r219977, "Re-commit r217995 and follow-up patches (r217997, r218011, r218053). These were"

It broke some builders. I guess it'd be reproducible with --vg.

  Failing Tests (3):
      Clang :: CXX/except/except.spec/p1.cpp
      Clang :: SemaTemplate/instantiate-exception-spec-cxx11.cpp
      Clang :: SemaTemplate/instantiate-exception-spec.cpp

llvm-svn: 220038