cmd/compile: improve atomic swap intrinsics on arm64

ARMv8.1 has added new instructions for atomic memory operations. This
change builds on the previous change which added support for atomic add,
0a7ac93c, to include similar support for
atomic-compare-and-swap, atomic-swap, atomic-or, and atomic-and
intrinsics. Since the new instructions are not guaranteed to be present,
we guard their usages with a branch on a CPU feature.

Peformance on an ARMv8.1 machine:
name                 old time/op  new time/op  delta
CompareAndSwap-16    37.9ns ±16%  24.1ns ± 4%  -36.44%  (p=0.000 n=10+9)
CompareAndSwap64-16  38.6ns ±15%  24.1ns ± 3%  -37.47%  (p=0.000 n=10+10)

name       old time/op  new time/op  delta
Swap-16    46.9ns ±32%  12.5ns ± 6%  -73.40%  (p=0.000 n=10+10)
Swap64-16  53.4ns ± 1%  12.5ns ± 6%  -76.56%  (p=0.000 n=10+10)

name            old time/op  new time/op  delta
Or8-16          8.81ns ± 0%  5.61ns ± 0%  -36.32%  (p=0.000 n=10+10)
Or-16           7.21ns ± 0%  5.61ns ± 0%  -22.19%  (p=0.000 n=10+10)
Or8Parallel-16  59.8ns ± 3%  12.5ns ± 2%  -79.10%  (p=0.000 n=10+10)
OrParallel-16   51.7ns ± 3%  12.5ns ± 2%  -75.84%  (p=0.000 n=10+10)

name             old time/op  new time/op  delta
And8-16          8.81ns ± 0%  5.61ns ± 0%  -36.32%  (p=0.000 n=10+10)
And-16           7.21ns ± 0%  5.61ns ± 0%  -22.19%  (p=0.000 n=10+10)
And8Parallel-16  59.1ns ± 6%  12.8ns ± 3%  -78.33%  (p=0.000 n=10+10)
AndParallel-16   51.4ns ± 7%  12.8ns ± 3%  -75.03%  (p=0.000 n=10+10)

Performance on an ARMv8.0 machine (no atomics instructions):
name                 old time/op  new time/op  delta
CompareAndSwap-16    61.3ns ± 0%  62.4ns ± 0%  +1.70%  (p=0.000 n=8+9)
CompareAndSwap64-16  62.0ns ± 3%  61.3ns ± 2%    ~     (p=0.093 n=10+10)

name       old time/op  new time/op  delta
Swap-16     127ns ± 2%   131ns ± 2%  +2.91%  (p=0.001 n=10+10)
Swap64-16   128ns ± 1%   131ns ± 2%  +2.43%  (p=0.001 n=10+10)

name            old time/op  new time/op  delta
Or8-16          14.9ns ± 0%  15.3ns ± 0%  +2.68%  (p=0.000 n=10+10)
Or-16           11.8ns ± 0%  12.3ns ± 0%  +4.24%  (p=0.000 n=10+10)
Or8Parallel-16   137ns ± 1%   144ns ± 1%  +4.97%  (p=0.000 n=10+10)
OrParallel-16    128ns ± 1%   136ns ± 1%  +6.34%  (p=0.000 n=10+10)

name             old time/op  new time/op  delta
And8-16          14.9ns ± 0%  15.3ns ± 0%  +2.68%  (p=0.000 n=10+10)
And-16           11.8ns ± 0%  12.3ns ± 0%  +4.24%  (p=0.000 n=10+10)
And8Parallel-16   134ns ± 2%   141ns ± 1%  +5.29%  (p=0.000 n=10+10)
AndParallel-16    125ns ± 2%   134ns ± 1%  +7.10%  (p=0.000 n=10+10)

Fixes #39304

Change-Id: Idaca68701d4751650be6b4bedca3d57f51571712
Reviewed-on: https://go-review.googlesource.com/c/go/+/234217


Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: fannie zhang <Fannie.Zhang@arm.com>