Updating Subjects definitions for attributes based on semantic handling. Removes Subjects for things we cannot currently check, adds Subjects for things we can, and rectifies most discrepancies. Since Subjects are not currently handled in tablegen, there are no functional changes with this patch.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195508 91177308-0d34-0410-b5e6-96231b3b80d8