Add #ifdef guards for some POSIX error symbols that Windows doesn't like.

Per buildfarm results.  It looks like the older the Windows version, the
more errno codes it hasn't got ...

src/backend/utils/error/elog.c

@@ -3254,28 +3254,38 @@ get_errno_symbol(int errnum)
 			return "E2BIG";
 		case EACCES:
 			return "EACCES";
+#ifdef EADDRINUSE
 		case EADDRINUSE:
 			return "EADDRINUSE";
+#endif
+#ifdef EADDRNOTAVAIL
 		case EADDRNOTAVAIL:
 			return "EADDRNOTAVAIL";
+#endif
 		case EAFNOSUPPORT:
 			return "EAFNOSUPPORT";
 #ifdef EAGAIN
 		case EAGAIN:
 			return "EAGAIN";
 #endif
+#ifdef EALREADY
 		case EALREADY:
 			return "EALREADY";
+#endif
 		case EBADF:
 			return "EBADF";
+#ifdef EBADMSG
 		case EBADMSG:
 			return "EBADMSG";
+#endif
 		case EBUSY:
 			return "EBUSY";
 		case ECHILD:
 			return "ECHILD";
+#ifdef ECONNABORTED
 		case ECONNABORTED:
 			return "ECONNABORTED";
+#endif
 		case ECONNREFUSED:
 			return "ECONNREFUSED";
 #ifdef ECONNRESET
@@ -3292,8 +3302,10 @@ get_errno_symbol(int errnum)
 			return "EFAULT";
 		case EFBIG:
 			return "EFBIG";
+#ifdef EHOSTUNREACH
 		case EHOSTUNREACH:
 			return "EHOSTUNREACH";
+#endif
 		case EIDRM:
 			return "EIDRM";
 		case EINPROGRESS:
@@ -3304,12 +3316,16 @@ get_errno_symbol(int errnum)
 			return "EINVAL";
 		case EIO:
 			return "EIO";
+#ifdef EISCONN
 		case EISCONN:
 			return "EISCONN";
+#endif
 		case EISDIR:
 			return "EISDIR";
+#ifdef ELOOP
 		case ELOOP:
 			return "ELOOP";
+#endif
 		case EMFILE:
 			return "EMFILE";
 		case EMLINK:
@@ -3334,16 +3350,20 @@ get_errno_symbol(int errnum)
 			return "ENOSPC";
 		case ENOSYS:
 			return "ENOSYS";
+#ifdef ENOTCONN
 		case ENOTCONN:
 			return "ENOTCONN";
+#endif
 		case ENOTDIR:
 			return "ENOTDIR";
 #if defined(ENOTEMPTY) && (ENOTEMPTY != EEXIST) /* same code on AIX */
 		case ENOTEMPTY:
 			return "ENOTEMPTY";
 #endif
+#ifdef ENOTSOCK
 		case ENOTSOCK:
 			return "ENOTSOCK";
+#endif
 #ifdef ENOTSUP
 		case ENOTSUP:
 			return "ENOTSUP";
@@ -3356,8 +3376,10 @@ get_errno_symbol(int errnum)
 		case EOPNOTSUPP:
 			return "EOPNOTSUPP";
 #endif
+#ifdef EOVERFLOW
 		case EOVERFLOW:
 			return "EOVERFLOW";
+#endif
 		case EPERM:
 			return "EPERM";
 		case EPIPE:
@@ -3372,10 +3394,14 @@ get_errno_symbol(int errnum)
 #endif
 		case ESRCH:
 			return "ESRCH";
+#ifdef ETIMEDOUT
 		case ETIMEDOUT:
 			return "ETIMEDOUT";
+#endif
+#ifdef ETXTBSY
 		case ETXTBSY:
 			return "ETXTBSY";
+#endif
 #if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
 		case EWOULDBLOCK:
 			return "EWOULDBLOCK";