building module 'Foo' imported from..." notes (the same we we provide
"In file included from..." notes) in the diagnostic, so that we know
how this module got included in the first place. This is part of
<rdar://problem/12696425>.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169021 91177308-0d34-0410-b5e6-96231b3b80d8