Darwin AArch64 application processors are run with Top Byte Ignore mode
enabled so metadata may be stored in the top byte, it needs to be
ignored when reading/writing memory. David Spickett handled this already
in the base class Process::ReadMemory but ProcessMachCore overrides that
method (to avoid the memory cache) and did not pick up the same change.
I add a test case that creates a pointer with metadata in the top byte
and dereferences it with a live process and with a corefile.
rdar://123784501
52557bce73