Provide sighandler_t fallback for non-GNU-libc platforms

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

lib/igt_core.c

@@ -1206,6 +1206,10 @@ void igt_waitchildren(void)
 #define MAX_SIGNALS		32
 #define MAX_EXIT_HANDLERS	10
 
+#ifndef HAVE_SIGHANDLER_T
+typedef void (*sighandler_t)(int);
+#endif
+
 static struct {
 	sighandler_t handler;
 	bool installed;