One of the conclusions of the discussion on D49740 was that SafeMachO is better
off in the Host module (as that's the only place which should include
mach/machine.h, which is what this header is working around). Also, Utility,
which is the only module which cannot include Host, should not be doing
anything with object file formats.
This patch implements that move, and also removes any unneded includes of that
I've verified that MacOS still compiles after this.