tools/nolibc: add helpers for wait() signal exits

These are useful for users and will also be used in an upcoming
testcase.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/include/nolibc/types.h

@@ -97,6 +97,8 @@
 /* Macros used on waitpid()'s return status */
 #define WEXITSTATUS(status) (((status) & 0xff00) >> 8)
 #define WIFEXITED(status)   (((status) & 0x7f) == 0)
+#define WTERMSIG(status)    ((status) & 0x7f)
+#define WIFSIGNALED(status) ((status) - 1 < 0xff)
 
 /* waitpid() flags */
 #define WNOHANG      1