patch 8.2.5113: timer becomes invalid after fork/exec, :gui gives errors

Problem:    Timer becomes invalid after fork/exec, :gui gives errors. (Gabriel
            Dupras)
Solution:   Delete the timer befor forking. (closes #10584)
diff --git a/src/proto/os_unix.pro b/src/proto/os_unix.pro
index 91024b1..268f3bf 100644
--- a/src/proto/os_unix.pro
+++ b/src/proto/os_unix.pro
@@ -88,4 +88,5 @@
 void xsmp_close(void);
 void stop_timeout(void);
 const int *start_timeout(long msec);
+void delete_timer(void);
 /* vim: set ft=c : */