[AST] Reduce Decl::getASTContext() calls.
 - This function is not at all free; pass it around along some hot paths instead
   of recomputing it deep inside various VarDecl methods.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@152363 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed