[Compiler-rt] Fix running ASan/TSan unit tests under macOS 12.0.

[delcypher]

Summary

On macOS the unit tests currently rely on libmalloc being used for
allocations (due to no functioning interceptors) but also having the
ASan/TSan allocator initialized in the same process.

This leads to crashes with the macOS 12.0 libmalloc nano allocator so
disable use of the allocator while running unit tests as a workaround.

rdar://80086125

compiler-rt/unittests/lit.common.unit.cfg.py

 if 'TEMP' in os.environ:
     config.environment['TEMP'] = os.environ['TEMP']
 
 if config.host_os == 'Darwin':
   # 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.
   lit_config.parallelism_groups["shadow-memory"] = 3
+  # Disable libmalloc nanoallocator due to crashes running on macOS 12.0.
+  #
+  # rdar://80086125
+  config.environment['MallocNanoZone'] = '0'
 
   # The test config gets pickled and sent to multiprocessing workers, and that
   # only works for code if it is stored at the top level of some module.
   # Therefore, we have to put the code in a .py file, add it to path, and import
   # it to store it in the config.
   import site
   site.addsitedir(os.path.dirname(__file__))
   import lit_unittest_cfg_utils
   config.darwin_sanitizer_parallelism_group_func = \
     lit_unittest_cfg_utils.darwin_sanitizer_parallelism_group_func