ppc64 has umode_t defined as int in asm/types.h, which is called
(in a roundabout way) from sys/wait.h via signal.h

Adding signal.h here lets the configure script find it, avoiding
breakage when it comes to building libgnome/gnome-exec.c

--- gnome-libs-1.4.2/configure	2007-10-25 11:51:18.000000000 +0100
+++ gnome-libs-1.4.2/configure	2007-10-25 12:27:30.000000000 +0100
@@ -11297,6 +11297,7 @@
 #include <stdlib.h>
 #include <stddef.h>
 #endif
+#include <signal.h>
 EOF
 if (eval "$ac_cpp conftest.$ac_ext") 2>&5 |
   egrep "(^|[^a-zA-Z_0-9])umode_t[^a-zA-Z_0-9]" >/dev/null 2>&1; then