Move the module auto-import logic after the logic that allows a

Move the module auto-import logic after the logic that allows a
callback client to suggest an alternative search path and after we
complain when the included file can't be found. The former can't be
tested in isolation, the latter doesn't actually matter (because we
won't make a module suggestion if no header is available). However,
the flow is better this way.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@145502 91177308-0d34-0410-b5e6-96231b3b80d8