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

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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150631 91177308-0d34-0410-b5e6-96231b3b80d8