cpu-exec: Move down some declarations in cpu_exec()

This will fix a compiler warning with -Wclobbered:

http://lists.nongnu.org/archive/html/qemu-devel/2016-07/msg03347.html

Reported-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Message-Id: <20160715193123.28113-1-sergey.fedorov@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

cpu-exec.c

@@ -608,17 +608,16 @@ int cpu_exec(CPUState *cpu)
     init_delay_params(&sc, cpu);
 
     for(;;) {
-        TranslationBlock *tb, *last_tb;
-        int tb_exit = 0;
-
         /* prepare setjmp context for exception handling */
         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
+            TranslationBlock *tb, *last_tb = NULL;
+            int tb_exit = 0;
+
             /* if an exception is pending, we execute it here */
             if (cpu_handle_exception(cpu, &ret)) {
                 break;
             }
 
-            last_tb = NULL; /* forget the last executed TB after exception */
             cpu->tb_flushed = false; /* reset before first TB lookup */
             for(;;) {
                 cpu_handle_interrupt(cpu, &last_tb);