core: Include cstring whenever strncpy is used (#7267)

Fixes ppc64le build in alpine

src/managers/EventManager.cpp

@@ -8,6 +8,7 @@
 #include <sys/types.h>
 #include <sys/un.h>
 #include <unistd.h>
+#include <cstring>
 
 CEventManager::CEventManager() {
     m_iSocketFD = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);