Insomniac refactoring: change how the parser allocates attributes so that

Insomniac refactoring:  change how the parser allocates attributes so that
AttributeLists do not accumulate over the lifetime of parsing, but are
instead reused.  Also make the arguments array not require a separate
allocation, and make availability attributes store their stuff in
augmented memory, too.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@128209 91177308-0d34-0410-b5e6-96231b3b80d8