Fix race in tst-mqueue5

[Tulio Magno Quites Machado Filho]

"Paul E. Murphy" <murphyp@linux.vnet.ibm.com> writes:

> The check is done on line 117 by a thread spawned
> from do_child(), forked from do_test().  This test
> generates a signal in the forked process.
>
> Either thread may handle the signal, and on ppc,
> it happens to be done on do_child, on the thread
> which is not doing the check on line 117.
>
> This exposes a race condition whereby the test
> incorrectly fails as the signal is caught during
> or after the check.
>
> This is mitigated by ensuring the signal is blocked
> in the child thread while thread is running.

Pushed as a3e5b4f.

-- 
Tulio Magno