[Inline] don't add noalias metadata for unknown objects.

The unidentified objects recognized in `getUnderlyingObjects` may
still alias to the noalias parameter because `getUnderlyingObjects`
may not check deep enough to get the underlying object because of
`MaxLookup`. The real underlying object for the unidentified object
 may still be the noalias parameter.

Originally Patched By: tingwang

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D127202