consolidate rt_sigsuspend()

* pull compat version alongside with the native one
* make little-endian compat variant just call the native
* don't bother with separate conditional for compat (both native and
compat are going to become unconditional very soon).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc kernel/compat.c
Simple merge

diff --cc kernel/signal.c
Simple merge