Restore TestRegisterVariables failure decorator for older Clang

The @expectedFailureClang decorator was removed in r236447, but it
seems to be fixed only with Clang 3.5+.

llvm-svn: 236614

lldb/test/lang/c/register_variables/TestRegisterVariables.py

@@ -18,6 +18,7 @@ class RegisterVariableTestCase(TestBase):
         self.const_variable()
 
     @dwarf_test
+    @expectedFailureClang(None, ['<', '3.5'])
     @expectedFailureGcc #xfail to get buildbot green, test failed with gcc4.8.2
     def test_with_dwarf_and_run_command(self):
         """Test expressions on register values."""