net/slirp.c: fix warning with _FORTIFY_SOURCE

CC    net/slirp.o
cc1: warnings being treated as errors
net/slirp.c: In function 'slirp_smb_cleanup':
net/slirp.c:470: error: ignoring return value of 'system', declared with attribute warn_unused_result
make: *** [net/slirp.o] Error 1
Signed-off-by: NKirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

net/slirp.c

@@ -464,10 +464,17 @@ int net_slirp_redir(const char *redir_str)
 static void slirp_smb_cleanup(SlirpState *s)
 {
     char cmd[128];
+    int ret;
 
     if (s->smb_dir[0] != '\0') {
         snprintf(cmd, sizeof(cmd), "rm -rf %s", s->smb_dir);
-        system(cmd);
+        ret = system(cmd);
+        if (!WIFEXITED(ret)) {
+            qemu_error("'%s' failed.\n", cmd);
+        } else if (WEXITSTATUS(ret)) {
+            qemu_error("'%s' failed. Error code: %d\n",
+                    cmd, WEXITSTATUS(ret));
+        }
         s->smb_dir[0] = '\0';
     }
 }