Tests: disable test of /proc filesystem on Darwin.

We don't have it. I'm not entirely sure "Posix" is a good name for that
directory, but perhaps we should see how it develops.

llvm-svn: 238874

compiler-rt/test/sanitizer_common/TestCases/Posix/lit.local.cfg

@@ -5,5 +5,5 @@ def getRoot(config):
 
 root = getRoot(config)
 
-if root.host_os in ['Windows']:
+if root.host_os in ['Windows', 'Darwin']:
   config.unsupported = True