hppa: fix sigaction decoding

hppa: fix sigaction decoding

Since the rt_sigaction syscall on hppa doesn't have a sa_restorer,
do not include it in the kernel struct.

We also have to undefine SA_RESTORER so that code doesn't try to
use it.  The headers will export this, but the syscall doesn't
actually respect it.

* signal.c (SA_RESTORER): Undefine when HPPA is defined.
(struct new_sigaction): Disable sa_restorer on hppa.