forkfd/linux: handle failure from sys_clone

Pick-to: 5.15
Change-Id: I98a28a816fdc089cefcbf8f42053ddffedc10cdf
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/3rdparty/forkfd/forkfd_linux.c

@@ -151,6 +151,8 @@ int system_forkfd(int flags, pid_t *ppid, int *system)
     if (flags & FFD_VFORK_SEMANTICS)
         cloneflags |= CLONE_VFORK;
     pid = sys_clone(cloneflags, &pidfd);
+    if (pid < 0)
+        return pid;
     if (ppid)
         *ppid = pid;