Fix a nasty bug in the type remapping stuff that I added that is breaking kc++ on

the build bot in some cases.  The basic issue happens when a source module contains
both a "%foo" type and a "%foo.42" type.  It will see the later one, check to see if
the destination module contains a "%foo" type, and it will return true... because
both the source and destination modules are in the same LLVMContext.  We don't want
to map source types to other source types, so don't do the remapping if the mapped
type came from the source module.

Unfortunately, I've been unable to reduce a decent testcase for this, kc++ is 
pretty great that way.

llvm-svn: 147010