Underlying condition for throttling is "has large mmap'd regions" (i.e.,
shadow memory) and not sanitizers in general (e.g., UBSan does not need
to be throttled).
Rename parallelism group `darwin-64bit-sanitizer` to `shadow-memory` and
apply it unconditionally to all tests which require it. We can then have
all the Darwin throttling logic in one place in the commen lit config.
Throttle sanitizer_common unit tests. Configuration was previously
missing from sanitizer_common/Unit/lit.site.cfg.
Reviewed by: kubamracek
Differential Revision: https://reviews.llvm.org/D58677
llvm-svn: 355018