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
 }