Convert block_gdbarch to method

This converts block_gdbarch to be a method.  This was mostly written
by script.

gdb/cp-namespace.c

@@ -197,7 +197,7 @@ cp_lookup_bare_symbol (const struct language_defn *langdef,
       if (block == NULL)
 	gdbarch = target_gdbarch ();
       else
-	gdbarch = block_gdbarch (block);
+	gdbarch = block->gdbarch ();
       sym.symbol
 	= language_lookup_primitive_type_as_symbol (langdef, gdbarch, name);
       sym.block = NULL;