Module Debugging: Emit the canonical debug info for Objective-C classes

in the compile unit that contains their implementation even if their
interface is declared in a module.

The private @implementation of an @interface may have additional
hidden ivars so we should not defer to the public version of the
type that is found in the module.

<rdar://problem/25541798>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@266937 91177308-0d34-0410-b5e6-96231b3b80d8