Do a little magic and a little greasework to make it much more efficient
to cast a DeclContext down to a specific implementation class.

There are still lots of calls to Decl::castFromDeclContext left, mostly
arising from DeclContext::getParent().



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@94786 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed