[dev.simd] simd: make 'go generate' generate everything
The simd package involves quite a lot of code generation.
Currently, that's spread across a few different tools.
Bring the process together in simd/_gen/main.go and make
'go generate' in the simd package do the right thing.
Change-Id: Iba7e120987f13840a23ed32a528e2398fc7a6065
Reviewed-on: https://go-review.googlesource.com/c/go/+/721663
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Austin Clements <austin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>