Don't have ProcessMachCore::CanDebug use the Target's arch when

creating the ModuleSpec to load the core file - we won't have a fat
core file and we can end up with cpu subtype mismatches if the core
file header isn't written out completely accurately.  We need to
be a little loose in this particular case.
<rdar://problem/17843388>

llvm-svn: 216498