sigpending(2) will never fail. Optimize the syscall stub accordingly like
authorkettenis <kettenis@openbsd.org>
Tue, 4 May 2021 19:02:52 +0000 (19:02 +0000)
committerkettenis <kettenis@openbsd.org>
Tue, 4 May 2021 19:02:52 +0000 (19:02 +0000)
commitc3e57ce1a9bef37ec8ff5fc82362bfd3a0573a2e
tree15938d4fb8c827a33488bd52b038f32e7c83ba4e
parent0dfc6687242ae960753fa876f2460b0a79ed678d
sigpending(2) will never fail.  Optimize the syscall stub accordingly like
we do on other architectures.

ok mpi@
lib/libc/arch/aarch64/sys/sigpending.S