signal() returns SIG_ERR, not just -1. The sys/signal.h header file

provides the cast from -1 to the signal() return type, so no further
casting by programmers should be required.

Pointed out by: bde (of course).

lib/libc/gen/signal.3

@@ -194,7 +194,7 @@ function;
 ignored signals remain ignored.
 .Sh RETURN VALUES
 The previous action is returned on a successful call.
-Otherwise, \-1 is returned and  the global variable
+Otherwise, SIG_ERR is returned and  the global variable
 .Va errno
 is set to indicate the error.
 .Sh ERRORS