This configure check fails for several  wrong reasons,
with misleading errors. Make it compile properly.

--- joe-4.7/acinclude.m4
+++ joe-4.7/acinclude.m4
@@ -59,9 +59,10 @@ AC_DEFUN([joe_REINSTALL_SIGHANDLERS],
 #include <signal.h>
 #endif
 
-#ifndef HAVE_SIGHANDLER_T
-typedef RETSIGTYPE (*sighandler_t)(int);
-#endif
+typedef void RETSIGTYPE;
+ 
+void set_signal(int signum, sighandler_t handler);
+RETSIGTYPE sigint(int s);
 
 int nsigint;