* fix mutex_trylock_fail test

projects/test_suite/mutex_trylock_fail.c

@@ -7,14 +7,14 @@
 
 mutex_t mutex;
 
-void second_thread(void) {
+static void second_thread(void) {
     puts(" 2nd: trying to lock mutex...");
     mutex_trylock(&mutex);
     puts(" 2nd: done.");
 }
 
-tcb second_tcb;
-char second_stack[KERNEL_CONF_STACKSIZE_MAIN];
+static tcb second_tcb;
+static char second_stack[KERNEL_CONF_STACKSIZE_MAIN];
 
 void mutex_trylock_fail(char* cmdline)
 {
@@ -22,7 +22,7 @@ void mutex_trylock_fail(char* cmdline)
     mutex_lock(&mutex);
 
     puts("main: creating thread...");
-    int pid = thread_create(&second_tcb, second_stack, KERNEL_CONF_STACKSIZE_MAIN, PRIORITY_MAIN-1, CREATE_STACKTEST, second_thread, "nr2");
+    thread_create(&second_tcb, second_stack, KERNEL_CONF_STACKSIZE_MAIN, PRIORITY_MAIN-1, CREATE_STACKTEST, second_thread, "nr2");
     
     puts("main: thread created. Unlocking mutex...");
     mutex_unlock(&mutex, true);