Removing a bit of custom parsing functionality used by the thread safety analysis APIs. Now using tablegen to determine whether an attribute's arguments should be parsed in an unevaluated context instead of relying on a separate, hard-coded list of attributes.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198883 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "Disable LeakSanitizer in TableGen binaries, see PR18325"

To declare or define reserved identifers is undefined behaviour in standard
C++. This needs to be addressed in compiler-rt before it can be used in LLVM.

See the list discussion for details.

This reverts commit r198858.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198885 91177308-0d34-0410-b5e6-96231b3b80d8