This is the meat of the code to add Clang modules

This is the meat of the code to add Clang modules
support to LLDB.  It includes the following:

- Changed DeclVendor to TypeVendor.
- Made the ObjCLanguageRuntime provide a DeclVendor
  rather than a TypeVendor.
- Changed the consumers of TypeVendors to use
  DeclVendors instead.
- Provided a few convenience functions on
  ClangASTContext to make that easier.

llvm-svn: 223433