x/build: test whether Go core changes break external tools and debuggers #18144
Changes to the Go core (compiler output, libraries, x/tools) can break tools and debuggers that build on them, such as gocode (@nsf), Delve (@derekparker), and Backtrace's ptrace (@abelmathew). While those tool authors can test for breakages against tip, it might be useful for us to know when CLs submitted to the Go core break tools that are important to the Go community. We should work with the authors to ensure the tools are fixed for each new Go release.
@bradfitz suggested we may be able to extend the builders to help with this testing.
This will allow long tests to use/test delve. Delve is built in its own stage with go1.12, then copied out. Updates golang/go#18144 Change-Id: I346729c945a95d5e34616500913a43bbe03b524c Reviewed-on: https://go-review.googlesource.com/c/build/+/172959 Reviewed-by: Brad Fitzpatrick <firstname.lastname@example.org>