Enabled the PlatformLinux and PlatforFreeBSD on MacOSX so they can be used

and also so we don't break them with our code changes.

The _only_ plug-ins that should be #ifdef'ed out and not compiled in LLDB
are those that only work when running natively on the host system.

This fixed bot the PlatformLinux and PlatformFreeBSD build breakages that
were due to ModuleSpec changes.

llvm-svn: 151539