mac arm64: Provide something more useful from SystemSnapshot::CPURevison
mac arm64: Provide something more useful from SystemSnapshot::CPURevison

hw.cputype is just CPU_TYPE_ARM64, which isn’t terribly useful.
hw.cpufamily is somewhat better as it uses <mach/machine.h> CPUFAMILY_*
values, which distinguish between different CPU generations.
CPUFAMILY_ARM_VORTEX_TEMPEST identifies A12, for example. (The fun cores
are Vortex and the boring cores are Tempest.)

Bug: crashpad:345
Change-Id: I88be4fa0b305b2fa15bd24358f63dc7d72192b27
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/2289041
Reviewed-by: Nico Weber <c0f02d98506190746d1cdcb01be0f37b51e27077@chromium.org>
Commit-Queue: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>

chromium/crashpad,chromium/crashpad,chromium/crashpad