Looks like we can't declare getpeereid on Windows anyway.

... for lack of the uid_t and gid_t typedefs.  Per buildfarm.

src/include/port.h

@@ -395,7 +395,7 @@ extern void srand48(long seed);
 extern int	getopt(int nargc, char *const * nargv, const char *ostr);
 #endif
 
-#ifndef HAVE_GETPEEREID
+#if !defined(HAVE_GETPEEREID) && !defined(WIN32)
 extern int	getpeereid(int sock, uid_t *uid, gid_t *gid);
 #endif