Explicitly check for LLVM 3.8 and 3.9 anomalies

Author: kulp

bindgen-integration/build.rs

@@ -83,7 +83,16 @@ impl ParseCallbacks for MacroCallback {
                 *self.seen_funcs.lock().unwrap() += 1;
             }
             "TESTMACRO_FUNCTIONAL_EMPTY(TESTMACRO_INTEGER)" => {
-                assert_eq!(value, &[] as &[&[u8]]);
+                // Early versions of libclang behave strangely for a function
+                // macro that expands to nothing, giving a `#` token as the
+                // expansion.
+                if cfg!(feature = "testing_only_libclang_3_8") ||
+                    cfg!(feature = "testing_only_libclang_3_9")
+                {
+                    assert_eq!(value, &[&[b'#']]);
+                } else {
+                    assert_eq!(value, &[] as &[&[u8]]);
+                }
                 *self.seen_funcs.lock().unwrap() += 1;
             }
             "TESTMACRO_FUNCTIONAL_TOKENIZED(a,b,c,d,e)" => {