[tsan] Enable the tsan/libcxx/ testcase(s) on Darwin

Apparently, the std_shared_ptr.cc testcase works fine on Darwin, even without the instrumented libcxx. Let's enable it.

Differential Revision: https://reviews.llvm.org/D26162

llvm-svn: 285634

compiler-rt/test/tsan/libcxx/lit.local.cfg

@@ -5,6 +5,8 @@ def getRoot(config):
 
 root = getRoot(config)
 
-if not root.has_libcxx:
+# Only run if we have an instrumented libcxx.  On Darwin, run always (we have
+# interceptors to support the system-provided libcxx).
+if not root.has_libcxx and root.host_os != 'Darwin':
   config.unsupported = True