[monitoring-plugins] Fix missing include in plugins/runcmd.c

[RincewindsHat]

 Module: monitoring-plugins
 Branch: master
 Commit: 09923e8a0ffd3540f7c950743ef6b60ea85fe9cd
 Author: RincewindsHat <12514511+RincewindsHat at users.noreply.github.com>
   Date: Sat Oct  7 23:31:59 2023 +0200
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugins/commit/?id=09923e8

Fix missing include in plugins/runcmd.c

---

 plugins/runcmd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/plugins/runcmd.c b/plugins/runcmd.c
index bc0a497..4f3e349 100644
--- a/plugins/runcmd.c
+++ b/plugins/runcmd.c
@@ -60,6 +60,8 @@
 # define SIG_ERR ((Sigfunc *)-1)
 #endif
 
+#include "../lib/maxfd.h"
+
 /* This variable must be global, since there's no way the caller
  * can forcibly slay a dead or ungainly running program otherwise.
  * Multithreading apps and plugins can initialize it (via NP_RUNCMD_INIT)