https://bugs.gentoo.org/900164
Patch from https://sourceforge.net/p/joe-editor/mercurial/merge-requests/3/

commit 26e83257075789d901cadbe280ff7f1bd7602983
Authored by: Nikita Popov 2023-01-31

   Port to C99

   Ensure that functions are declared before use for compatibility
   with newer compiler versions.

--- a/acinclude.m4
+++ b/acinclude.m4
@@ -9,7 +9,7 @@
 int main() {
   int a = 0;
   isblank(a++);
-  exit(a != 1);
+  return a != 1;
 }
 			],
 			[joe_cv_isblank=yes],
@@ -34,7 +34,7 @@
 #endif
 int main() {
 	/* exit succesfully if setpgrp() takes two args (*BSD systems) */
-	exit(setpgrp(0, 0) != 0);
+	return setpgrp(0, 0) != 0;
 }],
 			[joe_cv_setpgrp_void=no],
 			[joe_cv_setpgrp_void=yes],
@@ -95,7 +95,7 @@
 	kill((int)getpid(), SIGINT);
 	kill((int)getpid(), SIGINT);
 	/* exit succesfully if don't have to reinstall sighandler when invoked */
-	exit(nsigint != 2);
+	return nsigint != 2;
 }],
 			[joe_cv_reinstall_sighandlers=no],
 			[joe_cv_reinstall_sighandlers=yes],
--- a/joe/selinux.c
+++ b/joe/selinux.c
@@ -6,6 +6,7 @@
 
 #ifdef WITH_SELINUX
 #include <selinux/selinux.h>
+#include <error.h>
 static int selinux_enabled = -1;
 #endif
 
@@ -108,7 +109,7 @@
 		return 0;
 
 	if (setfscreatecon(0) < 0) {
-		error(0, errno, joe_gettext(_("Could not reset default security context")));
+		error(0, errno, "%s", joe_gettext(_("Could not reset default security context")));
 		return 1;
 	}
 #endif