add //go:build lines

[shogo82148]

I ran go1.17rc fmt
See https://tip.golang.org/doc/go1.17#gofmt for more details.

gofmt (and go fmt) now synchronizes //go:build lines with // +build lines. If a file only has // +build lines, they will be moved to the appropriate location in the file, and matching //go:build lines will be added. Otherwise, // +build lines will be overwritten based on any existing //go:build lines. For more information, see https://golang.org/design/draft-gobuild.

[mattn]

LGTM

[mattn]

Thank you