utils: In Solaris, avoid a warning about an unused variable.

When HAVE_GETHOSTBYNAME_R_5 was set by the script ./configure, GCC 7.3.0 found
an unused variable. Actually, the variable was used (set to a dummy value) but
the compiler optimization might have removed that. Instead, this change ensures
that the variable 'res' is only used when it is really required.

Change-Id: Ic3ea23ccf84ac4bc2d501b514985b989030abab5

main/utils.c

@@ -196,7 +196,9 @@ static int gethostbyname_r (const char *name, struct hostent *ret, char *buf,
 */
 struct hostent *ast_gethostbyname(const char *host, struct ast_hostent *hp)
 {
+#ifndef HAVE_GETHOSTBYNAME_R_5
 	int res;
+#endif
 	int herrno;
 	int dots = 0;
 	const char *s;
@@ -206,7 +208,6 @@ struct hostent *ast_gethostbyname(const char *host, struct ast_hostent *hp)
 	   integers, we break with tradition and refuse to look up a
 	   pure integer */
 	s = host;
-	res = 0;
 	while (s && *s) {
 		if (*s == '.')
 			dots++;