[test] Enable LeakSanitizer on 64-bit Darwin ASan llvm builds

[fjricci]

Summary

Also disables leak checking on lto tests, due to many leaks reported
in the system's ld64.

[vsk]

LGTM, thanks!

[fjricci]

Updating this because the lit setup changed

test/tools/lto/lit.local.cfg

 if not ('ld64_plugin' in config.available_features and 'X86' in config.root.targets):
     config.unsupported = True
+
+# These tests invoke ld64 from the system, which is not leak-free
+if "Address" in config.llvm_use_sanitizer:
+    config.environment['ASAN_OPTIONS'] = 'detect_leaks=0'

utils/lit/lit/llvm/config.py

def __init__(self, lit_config, config):
 
         # Check if we should run long running tests.
         long_tests = lit_config.params.get("run_long_tests", None)
         if lit.util.pythonize_bool(long_tests):
             features.add("long_tests")
 
         target_triple = getattr(config, 'target_triple', None)
         if target_triple:
+            if re.match(r'^x86_64.*-apple', target_triple):
+                if 'address' in sanitizers:
+                    self.with_environment('ASAN_OPTIONS', 'detect_leaks=1', append_path=True)
             if re.match(r'^x86_64.*-linux', target_triple):
                 features.add("x86_64-linux")
             if re.match(r'.*-win32$', target_triple):
                 features.add('target-windows')
 
         use_gmalloc = lit_config.params.get('use_gmalloc', None)
         if lit.util.pythonize_bool(use_gmalloc):
             # Allow use of an explicit path for gmalloc library.