On Darwin, we want to limit the parallelism during test execution for
sanitizer tests that use shadow memory. The reason is explained by this
existing comment:
> Only run up to 3 processes that require shadow memory simultaneously
> on 64-bit Darwin. Using more scales badly and hogs the system due to
> inefficient handling of large mmap'd regions (terabytes) by the
> kernel.
Previously we detected 3 cases:
* on-device: limit to 1 process
* 64-bit: macOS & simulators, limit to 3 processes
* others (32-bit): no limitation
We checked for the 64-bit case like this: `if arch in ['x86_64',
'x86_64h']` which misses macOS running on AS. Additionally, we don't
care about 32-bit anymore, so I've simplified this to 2 cases: on-device
and everything else.
Differential Revision: https://reviews.llvm.org/D122751
a5228bcaad