nptl: PTHREAD_COND_INITIALIZER compatibility with pre-2.41 versions (bug 32786)

nptl: PTHREAD_COND_INITIALIZER compatibility with pre-2.41 versions (bug 32786)

[BZ #25847]

The new initializer and struct layout does not initialize the
__g_signals field in the old struct layout before the change in
commit c36fc50781995e6758cae2b6927839d0157f213c ("nptl: Remove
g_refs from condition variables").  Bring back fields at the end
of struct __pthread_cond_s, so that they are again zero-initialized.

(cherry picked from commit dbc5a50d12eff4cb3f782129029d04b8a76f58e7)

Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>