cmd/compile: simplify negative on multiplication

cmd/compile: simplify negative on multiplication

goos: linux
goarch: amd64
pkg: cmd/compile/internal/test
cpu: AMD EPYC 7532 32-Core Processor
               │       simplify_base │               simplify_new          │
               │       sec/op        │   sec/op     vs base                │
SimplifyNegMul           623.0n ± 0%   319.3n ± 1%  -48.75% (p=0.000 n=10)

goos: linux
goarch: riscv64
pkg: cmd/compile/internal/test
cpu: Spacemit(R) X60
               │       simplify.base │               simplify.new          │
               │       sec/op        │   sec/op     vs base                │
SimplifyNegMul          10.928µ ± 0%   6.432µ ± 0%  -41.14% (p=0.000 n=10)

Change-Id: I1d9393cd19a0b948a5d3a512d627cdc0cf0b38be
Reviewed-on: https://go-review.googlesource.com/c/go/+/721520
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>