Actually, it's not that hard to merge the Windows pqsignal code ...

... just need to typedef sigset_t and provide sigemptyset/sigfillset,
which are easy enough.

src/backend/libpq/pqsignal.c

@@ -18,15 +18,10 @@
 #include "libpq/pqsignal.h"
 
 
-#ifndef WIN32
+/* Global variables */
 sigset_t	UnBlockSig,
 			BlockSig,
 			StartupBlockSig;
-#else
-int			UnBlockSig,
-			BlockSig,
-			StartupBlockSig;
-#endif
 
 
 /*
@@ -45,8 +40,6 @@ int			UnBlockSig,
 void
 pqinitmask(void)
 {
-#ifndef WIN32
-
 	sigemptyset(&UnBlockSig);
 
 	/* First set all signals, then clear some. */
@@ -101,19 +94,4 @@ pqinitmask(void)
 #ifdef SIGALRM
 	sigdelset(&StartupBlockSig, SIGALRM);
 #endif
-#else							/* WIN32 */
-	/* Set the signals we want. */
-	UnBlockSig = 0;
-	BlockSig = sigmask(SIGQUIT) |
-		sigmask(SIGTERM) | sigmask(SIGALRM) |
-	/* common signals between two */
-		sigmask(SIGHUP) |
-		sigmask(SIGINT) | sigmask(SIGUSR1) |
-		sigmask(SIGUSR2) | sigmask(SIGCHLD) |
-		sigmask(SIGWINCH) | sigmask(SIGFPE);
-	StartupBlockSig = sigmask(SIGHUP) |
-		sigmask(SIGINT) | sigmask(SIGUSR1) |
-		sigmask(SIGUSR2) | sigmask(SIGCHLD) |
-		sigmask(SIGWINCH) | sigmask(SIGFPE);
-#endif
 }

src/include/libpq/pqsignal.h

@@ -16,27 +16,24 @@
 #include <signal.h>
 
 #ifndef WIN32
-extern sigset_t UnBlockSig,
-			BlockSig,
-			StartupBlockSig;
-
 #define PG_SETMASK(mask)	sigprocmask(SIG_SETMASK, mask, NULL)
-#else							/* WIN32 */
-/*
- * Windows doesn't provide the POSIX signal API, so we use something
- * approximating the old BSD signal API.
- */
-extern int	UnBlockSig,
-			BlockSig,
-			StartupBlockSig;
+#else
+/* Emulate POSIX sigset_t APIs on Windows */
+typedef int sigset_t;
 
 extern int	pqsigsetmask(int mask);
 
 #define PG_SETMASK(mask)		pqsigsetmask(*(mask))
+#define sigemptyset(set)		(*(set) = 0)
+#define sigfillset(set)			(*(set) = ~0)
 #define sigaddset(set, signum)	(*(set) |= (sigmask(signum)))
 #define sigdelset(set, signum)	(*(set) &= ~(sigmask(signum)))
 #endif   /* WIN32 */
 
+extern sigset_t UnBlockSig,
+			BlockSig,
+			StartupBlockSig;
+
 extern void pqinitmask(void);
 
 #endif   /* PQSIGNAL_H */