Support attribute between double pointer stars

"int * __attribute__((something)) *" is supported by GCC.

tests/tcctest.c

@@ -3031,3 +3031,10 @@ void attrib_test(void)
 	 sizeof(spacked), sizeof(Spacked2), sizeof(spacked2));
 #ifdef BROKEN
   printf("attr: %d %d\n", sizeof(Spacked3), sizeof(spacked3));
+#endif
+}
+extern __attribute__((__unused__)) char * __attribute__((__unused__)) *
+strange_attrib_placement (void);
+
+void * __attribute__((__unused__)) get_void_ptr (void *a)
+{