[Sanitizer] Disable LSan when testing on iOS simulators

[yln]

Summary

LSan (ASAN_OPTIONS=detect_leaks=1) is supported on macOS, but disabled
by default on Darwin (SANITIZER_MAC):

COMMON_FLAG(bool, detect_leaks, !SANITIZER_MAC, "Enable memory leak detection.")

We enable it here for ASan tests to prevent regressions (per comment).
However, LSan is not supported for the iOS simulator and the tests fail
when it is enabled.

Make this "Is macOS?" check more precise since the current one (`Darwin
&& x86_64`) has two issues:

• Includes the simulators
• Excludes macOS on Apple Silicon

This will allow us to (re)enable simulator testing on Green dragon to
give open source better feedback about sanitizer changes:
https://green.lab.llvm.org

rdar://86529234

[delcypher]

LGTM

compiler-rt/test/asan/lit.cfg.py

if platform.system() == 'SunOS':
     config.environment[dynamic_library_lookup_var] = new_ld_library_path_64
 
 # Setup config name.
 config.name = 'AddressSanitizer' + config.name_suffix
 
 # Platform-specific default ASAN_OPTIONS for lit tests.
 default_asan_opts = list(config.default_sanitizer_opts)
 
-# On Darwin, leak checking is not enabled by default. Enable for x86_64
+# On Darwin, leak checking is not enabled by default. Enable on macOS
 # tests to prevent regressions
-if config.host_os == 'Darwin' and config.target_arch == 'x86_64':
+if config.host_os == 'Darwin' and config.apple_platform == 'osx':
   default_asan_opts += ['detect_leaks=1']
 
 default_asan_opts_str = ':'.join(default_asan_opts)
 if default_asan_opts_str:
   config.environment['ASAN_OPTIONS'] = default_asan_opts_str
   default_asan_opts_str += ':'
 config.substitutions.append(('%env_asan_opts=',
                              'env ASAN_OPTIONS=' + default_asan_opts_str))

 
 # Fast unwinder doesn't work with Thumb
 if not config.arm_thumb:
   config.available_features.add('fast-unwinder-works')
 
 # Turn on leak detection on 64-bit Linux.
 leak_detection_android = config.android and 'android-thread-properties-api' in config.available_features and (config.target_arch in ['x86_64', 'i386', 'i686', 'aarch64'])
 leak_detection_linux = (config.host_os == 'Linux') and (not config.android) and (config.target_arch in ['x86_64', 'i386', 'riscv64'])
-leak_detection_mac = (config.host_os == 'Darwin') and (config.target_arch == 'x86_64')
+leak_detection_mac = (config.host_os == 'Darwin') and (config.apple_platform == 'osx')
 leak_detection_netbsd = (config.host_os == 'NetBSD') and (config.target_arch in ['x86_64', 'i386'])
 if leak_detection_android or leak_detection_linux or leak_detection_mac or leak_detection_netbsd:
   config.available_features.add('leak-detection')
 
 # Set LD_LIBRARY_PATH to pick dynamic runtime up properly.
 push_dynamic_library_lookup_path(config, config.compiler_rt_libdir)
 
 # GCC-ASan uses dynamic runtime by default.