Always enable C line in traceback for tests (GH-3098)

runtests.py

@@ -1096,6 +1096,11 @@ class CythonCompileTestCase(unittest.TestCase):
                 from Cython.Build.Dependencies import update_pythran_extension
                 update_pythran_extension(extension)
 
+            # Compile with -DCYTHON_CLINE_IN_TRACEBACK=1 unless we have
+            # the "traceback" tag
+            if 'traceback' not in self.tags['tag']:
+                extension.define_macros.append(("CYTHON_CLINE_IN_TRACEBACK", 1))
+
             for matcher, fixer in list(EXT_EXTRAS.items()):
                 if isinstance(matcher, str):
                     # lazy init

tests/run/tracebacks.pyx

-import traceback
+# tag: traceback
 
 def foo1():
   foo2()
@@ -21,6 +21,7 @@ def test_traceback(cline_in_traceback=None):
   try:
     foo1()
   except:
+    import traceback
     tb_string = traceback.format_exc()
     expected = (
       'tracebacks.pyx',