[release-branch.go1.19] cmd/go/internal/imports: recognize "unix" build tag
For #20322
For #51572
Updates #54712
Fixes #54736
Change-Id: I22fcfa820e83323bfdf1a40deee7286240f02b3e
GitHub-Last-Rev:
cd2c6536b0298baf3c54e5bdbc456a814545cff4
GitHub-Pull-Request: golang/go#54716
Reviewed-on: https://go-review.googlesource.com/c/go/+/426296
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
(cherry picked from commit
3c6a5cdb9a29c0e3b12cdaa8ab81ba22d989e3b0)
Reviewed-on: https://go-review.googlesource.com/c/go/+/426814
Run-TryBot: Bryan Mills <bcmills@google.com>