This reverts commit r206413.
This was proposed before, but it's not clear if this is really a good
idea:
http://reviews.llvm.org/D3034
llvm-svn: 206415
This allows clang to parse the type_traits header in Visual Studio 2012,
which is included widely in practice.
This is a rework of r163022 by João Matos. The original patch broke
preprocessing of gtest headers, which this patch addresses.
Patch by Will Wilson!
llvm-svn: 184968