Do not rely on implicit int declarations, a feature removed in C99.

This was fixed upstream by rewriting the code by eliminating old-style
function declarations: <https://sourceforge.net/p/tkimg/code/459/>

diff --git a/sgi/sgi.c b/sgi/sgi.c
index 059f65403be19b15..2bd0ea000e6a2ac4 100644
--- a/sgi/sgi.c
+++ b/sgi/sgi.c
@@ -237,6 +237,7 @@ static int putrow(IMAGE *image, unsigned short *buffer,
 */
 static void i_errhdlr(fmt, a1, a2, a3, a4)  /* most args currently used is 2 */
 char *fmt;
+int a1, a2, a3, a4;
 {
     /* fprintf(stderr, fmt); */
     return;