Change Platform::GetRemoteSharedModule so if it's given a ModuleSpec

Change Platform::GetRemoteSharedModule so if it's given a ModuleSpec
which specifies a file path and UUID but not an architecture, open
the file at that path and try every one of the architectures in the
file to see if there is a UUID match.  Currently we'll pick the
first slice of a multi-architecture file and return that as the
match, and when the UUID doesn't match because it's the wrong
architecture, we'll end up ignoring the file.

<rdar://problem/28487804>

llvm-svn: 283295