Summary:
We previously disallowed use of undocumented attributes with #pragma clang
attribute, but the justification for doing so was weak and it prevented many
reasonable use cases.
Reviewers: aaron.ballman, arphaman
Subscribers: cfe-commits, rnk, benlangmuir, dexonsmith, erik.pilkington
Differential Revision: https://reviews.llvm.org/D51507
llvm-svn: 341437