rt_sigaction, rt_sigprocmask, rt_sigsuspend: cleanup

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
rt_sigaction, rt_sigprocmask01, rt_sigsuspend: use rt_sigaction wrapper

These testcases use many pieces of duplicated code to test
syscall(__NR_rt_sigaction). Thus it's not beautiful to add support
for other architectures there.

To overcome this I:
 * moved everything inside '#ifdef LTP_RT_SIG_TEST' to a separate
   header file - 'include/lapi/rt_sigaction.h'
   So if we need to test the rt_sigaction syscall, we include 'lapi/sigaction.h',
   otherwise - include 'ltp_signal.h'.

 * moved struct kernel_sigaction out of '#ifdef __x86_64__', because
   it is not specific only for x86_64

 * implemented a wrapper for the rt_sigaction syscall and put it
   into 'include/lapi/rt_sigaction.h'

 * modified the above test cases to use this wrapper

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
ltp_rt_sigaction.h: added SPARC support

syscall(__NR_rt_sigaction) on SPARC requires more arguments, than
it does in x86_64 environment.

Therefore to make ltp_rt_sigaction() work on SPARC, we modify it
the same way as it's done in glibc, i.e. by hiding the additional
argument - the stub - inside the wrapper.

Based on patches by Jose E. Marchesi <jose.marchesi@oracle.com>.

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>