Emulate sigprocmask(), not sigsetmask(), on Windows.

Since commit a65e0864, we've required Unix systems to have
sigprocmask().  As noted in that commit's message, we were still
emulating the historical pre-standard sigsetmask() function in our
Windows support code.  Emulate standard sigprocmask() instead, for
consistency.

The PG_SETMASK() abstraction is now redundant and all calls could in
theory be replaced by plain sigprocmask() calls, but that isn't done by
this commit.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/3153247.1657834482%40sss.pgh.pa.us

src/backend/port/win32/signal.c

@@ -112,7 +112,7 @@ pgwin32_signal_initialize(void)
 /*
  * Dispatch all signals currently queued and not blocked
  * Blocked signals are ignored, and will be fired at the time of
- * the pqsigsetmask() call.
+ * the pqsigprocmask() call.
  */
 void
 pgwin32_dispatch_queued_signals(void)
@@ -154,12 +154,29 @@ pgwin32_dispatch_queued_signals(void)
 
 /* signal masking. Only called on main thread, no sync required */
 int
-pqsigsetmask(int mask)
+pqsigprocmask(int how, const sigset_t *set, sigset_t *oset)
 {
-	int			prevmask;
+	if (oset)
+		*oset = pg_signal_mask;
 
-	prevmask = pg_signal_mask;
-	pg_signal_mask = mask;
+	if (!set)
+		return 0;
+
+	switch (how)
+	{
+		case SIG_BLOCK:
+			pg_signal_mask |= *set;
+			break;
+		case SIG_UNBLOCK:
+			pg_signal_mask &= ~*set;
+			break;
+		case SIG_SETMASK:
+			pg_signal_mask = *set;
+			break;
+		default:
+			errno = EINVAL;
+			return -1;
+	}
 
 	/*
 	 * Dispatch any signals queued up right away, in case we have unblocked
@@ -167,7 +184,7 @@ pqsigsetmask(int mask)
 	 */
 	pgwin32_dispatch_queued_signals();
 
-	return prevmask;
+	return 0;
 }
 
 

src/include/libpq/pqsignal.h

@@ -15,15 +15,18 @@
 
 #include <signal.h>
 
-#ifndef WIN32
 #define PG_SETMASK(mask)	sigprocmask(SIG_SETMASK, mask, NULL)
-#else
+
+#ifdef WIN32
 /* Emulate POSIX sigset_t APIs on Windows */
 typedef int sigset_t;
 
-extern int	pqsigsetmask(int mask);
+extern int	pqsigprocmask(int how, const sigset_t *set, sigset_t *oset);
 
-#define PG_SETMASK(mask)		pqsigsetmask(*(mask))
+#define SIG_BLOCK				1
+#define SIG_UNBLOCK				2
+#define SIG_SETMASK				3
+#define sigprocmask(how, set, oset) pqsigprocmask((how), (set), (oset))
 #define sigemptyset(set)		(*(set) = 0)
 #define sigfillset(set)			(*(set) = ~0)
 #define sigaddset(set, signum)	(*(set) |= (sigmask(signum)))