util: Suppress a warning by adding CONST_CAST

Suppress a gcc warning which was introduced by
commit e0b48482c1.
("util: create a copy of program_name")
I guess MSVC doesn't have a corresponding warning.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Acked-by: Lorand Jakab <lojakab@cisco.com>

lib/util.c

@@ -455,7 +455,7 @@ void
 set_program_name__(const char *argv0, const char *version, const char *date,
                    const char *time)
 {
-    free(program_name);
+    free(CONST_CAST(char *, program_name));
 
 #ifdef _WIN32
     char *basename;