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>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@216498 91177308-0d34-0410-b5e6-96231b3b80d8