Add go 1.16 version.

[armfazh]

Adds go1.16 version for testing.

[armfazh]

todo; To investigate clobbered registers in dillithium assembler code.

[bwesterb]

It's an issue with avo: mmcloughlin/avo#156

[claucece]

I also have it happening in kyber:

pke/kyber/internal/common/amd64.s:1448:1: frame pointer is clobbered before saving

The HasSha3 does not exist anymore (in simd/keccakf1600/f1600x.go) in arm64 on go.16 as well:

// IsEnabledX2 returns true if the architecture supports a two-way SIMD
// implementation provided in this package.
func IsEnabledX2() bool { return cpu.ARM64.HasSHA3 }

We are using the x/sys one, but it might be bumped down there too: golang/go@6b66b59#diff-52c997d62192731381cdec487ea0eb77390c9ea5941e4d3ac4c9109c272417f6

@bwesterb bwesterb

[claucece]

Sort of did something around it here: claucece/go-exp@de5ce64

following https://go-review.googlesource.com/c/go/+/248260/2/src/internal/bytealg/index_amd64.s

[armfazh]

@cjpatton @claucece please take a look.

[claucece]

LGTM ;) Thanks!

[cjpatton]

LGTM