+#undef signal
+#define signal(SIG,ACT) sys_signal(SIG,ACT)
+
+/* Whether this is what all systems want or not, this is what
+ appears to be assumed in the source, for example data.c:arith_error. */
+typedef RETSIGTYPE (*signal_handler_t) (/*int*/);
+
+signal_handler_t sys_signal P_ ((int signal_number, signal_handler_t action));
+sigset_t sys_sigblock P_ ((sigset_t new_mask));
+sigset_t sys_sigunblock P_ ((sigset_t new_mask));
+sigset_t sys_sigsetmask P_ ((sigset_t new_mask));
+
+#define sys_sigdel(MASK,SIG) sigdelset (&MASK,SIG)
+
+#else /* ! defined (POSIX_SIGNALS) */
+#ifdef USG5_4