Never cache the result of a module file lookup.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174744 91177308-0d34-0410-b5e6-96231b3b80d8
Always keep highest identifier, selector, and macro IDs when we've
read another one, just as we do for types.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174745 91177308-0d34-0410-b5e6-96231b3b80d8