[Doc parsing] Add availability information to generated Comment XML.
(I still need to add a test once I figure it out).
Reviewed off-line by Doug. // rdar://12378879


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164861 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed