Add a completed/incomplete type difference. This allows us to have

partial types for contexts and forward decls while allowing us to
complete types later on for debug purposes.

This piggy-backs on the metadata replacement and rauw changes
for temporary nodes and takes advantage of the incremental
support I added in earlier. This allows us to, if we decide,
to limit adding methods and variables to structures in order
to limit the amount of debug information output into a .o file.

The caching is a bit complicated though so any thoughts on
untangling that are welcome.

llvm-svn: 150631