Fixed the remaining test suite failures after the recent objective C cleanup

and fixes we did. Now that objective C classes are represented by symbols with
their own type, there were a few more places in the objective C code that needed
to be fixed when searching for dynamic types.

Cleaned up the objective C runtime plug-in a bit to not keep having to create
constant strings and make one less memory access when we find an "isa" in the
objective C cache.

llvm-svn: 145799