Any time ProcessGDBRemote tries to get the remote's ProcessArchitecture,
it needs to fall back to using the HostArchitecture if a valid one is not
returned.  When doing low-level system debugging we may not have a process
(or the remote stub may not support the qProcessInfo packet) in which case
we should fall back to the architecture we determined via qHostInfo.
<rdar://problem/15713180>