[modules] When explicitly importing a module, it's fine for the imported module
to be newer than we were expecting. That happens if .pcm's get moved between
file systems during a distributed build. (It's still not OK for them to actually
be different, though, so we still check the size and signature matches.)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@222507 91177308-0d34-0410-b5e6-96231b3b80d8