Backport x/sys upgrade to 0.16 release to support go 1.17

[stefanb]

Backport just x/sys upgrade from c99d6e1 to v0.16-release branch so that next 1.16.* release will support go 1.17.

More context:

• blocking go 1.17 Homebrew/homebrew-core#83413
• Go issue runtime: unexpected signal during runtime execution in Go 1.17 but not Go 1.16 golang/go#46763
• elvish issue [crash] fatal error: unexpected signal during runtime execution #1389
• workaround elvish: Fix crash on go 1.17 macports/macports-ports#11983
• workaround elvish: support go 1.17 Homebrew/homebrew-core#83995

After merging it please:

• make / tag a new release (eg v0.16.2 on v0.16-release branch)

Simpler alternative to #1388
Fixes #1389

Altrenatively you can make a new release branch (eg v0.17-release) from the master branch somewhere after c99d6e1 and tag a new release (eg v0.17.0) there, but that might include other, unrelated changes.

[xiaq]

I've tagged v0.16.2 too.

[stefanb]

Thanks, @xiaq !

[xiaq]

Hmm, this broke the building of the website because the x/sys dependency was not in website/go.mod.

I'll fix that and bump to 0.16.3...

[stefanb]

Tnx! I was testing using Makefile and all tests passed as in CI. With initial PR #1388 on master i updated both go.mod files 😇