Better living through metaprogramming. Create a base class which abstracts

most of the unsafe boilerplate out of TypeLoc.  Create a QualifiedLoc class
to represent the idea that we *might* start representing source locations
of qualifiers.  Dealing with qualifiers explicitly like this also lets us
efficiently ignore them in all the concrete cases.

This should make it obvious and easy to add new TypeLoc subclasses.

llvm-svn: 84168