[dev.simd] simd: initialize directory to make it suitable for testing SIMD
this is a multistep operation between two repos to coordinate
this move. First copy internal/simd top simd (and adjust so
that it works with future generated SIMD), after this lands,
update golang/arch/internal/simdgen to target this directory
and add it to the end-to-end test (which will also be added
once it works and is truly end-to-end), finally remove internal/simd
once the updated generator has been submitted.
Change-Id: If372baadc0c02e47cc32bc55b39ac19d551b2b21
Reviewed-on: https://go-review.googlesource.com/c/go/+/676955
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Junyang Shao <shaojunyang@google.com>