[python] [tests] Fix test_linkage for unique external linkage

[mgorny]

Summary

Starting with r314037, anonymous namespaces no longer give
unique-external linkage to variables. However, this linkage can still be
achieved by using a type which is not exterally visible,
e.g. through being declared in an anonymous namespace but used outside
it. Fix the test to take advantage of that.

[mgorny]

Duplicate of D39161.

[mgorny]

Yay, I've found a way to get the desired linkage! ;-)

[aaron.ballman]

LGTM!

bindings/python/tests/cindex/test_linkage.py

 
 class TestLinkage(unittest.TestCase):
     def test_linkage(self):
         """Ensure that linkage specifers are available on cursors"""
 
         tu = get_tu("""
 void foo() { int no_linkage; }
 static int internal;
-namespace { extern int unique_external; }
+namespace { struct unique_external_type {} }
+unique_external_type unique_external;
 extern int external;
 """, lang = 'cpp')
 
         no_linkage = get_cursor(tu.cursor, 'no_linkage')
         self.assertEqual(no_linkage.linkage, LinkageKind.NO_LINKAGE)
 
         internal = get_cursor(tu.cursor, 'internal')
         self.assertEqual(internal.linkage, LinkageKind.INTERNAL)
 
         unique_external = get_cursor(tu.cursor, 'unique_external')
         self.assertEqual(unique_external.linkage, LinkageKind.UNIQUE_EXTERNAL)
 
         external = get_cursor(tu.cursor, 'external')
         self.assertEqual(external.linkage, LinkageKind.EXTERNAL)