add test case for hash enum name

Author: qinghon

bindgen-tests/tests/expectations/tests/enum_unnamed.rs

@@ -0,0 +1,10 @@
+// bindgen-flags: --hash-unnamed-enum
+
+enum {
+        A = 1,                                                                                                                                                                                  
+        B = 2                                                                                                                                                                                   
+};                                                                                                                                                                                              
+enum {                                                                                                                                                                                          
+        C = -3,                                                                                                                                                                                 
+        D = 4,                                                                                                                                                                                  
+};