Fail test when expected C compiler error not encountered.

runtests.py

@@ -869,9 +869,14 @@ class CythonCompileTestCase(unittest.TestCase):
         if not self.cython_only:
             try:
                 so_path = self.run_distutils(test_directory, module, workdir, incdir)
-            except:
+                compiled = True
+            except Exception:
+                compiled = False
                 if expected_errors != '_FAIL_C_COMPILE':
                     raise
+            if compiled and expected_errors == '_FAIL_C_COMPILE':
+                # must raise this outside the try block
+                raise RuntimeError('should have failed C compile')
         return so_path
 
 class CythonRunTestCase(CythonCompileTestCase):