Golang x/build/cmd/retrybuilds: support wiping non-"go" repos

x/build/cmd/retrybuilds has a comment:

// Only the main go repo is currently supported.

Likewise, the dashboard's clear results handler:

// clearResultsHandler purge a single build failure from the dashboard.                                                                                                                             
// It currently only supports the main Go repo.                                                                                                                                                     
func clearResultsHandler(r *http.Request) (interface{}, error) {                                 
...
        _, err := datastoreClient.RunInTransaction(ctx, func(tx *datastore.Transaction) error {
                c := &Commit{
                        PackagePath: "", // TODO(adg): support clearing sub-repos                                                                                                                   
...

Likewise, the dashboard's failures view (as used by retrybuilds) only lists the main repo.

All three would need love.

Comment From: darkLord19

Hey @bradfitz , I'd like to take on this issue but I don't have much idea about x/build so, can you give some pointers on the same. That'd be very helpful.

Comment From: bradfitz

@darkLord19, sorry, I don't have time to mentor somebody outside the Go team through this codebase. From past experience, ongoing contributors to x/build are extremely few & far between (despite people's ambitions & intentions) and any time invested in teaching people how to hack on this codebase doesn't pay off. (That is, it's much faster to do it myself, and I'm not currently prioritizing it.)

That said, I'm not saying we won't take a change from you for this, but you'll need to put in the effort to learn the codebase yourself first.

Comment From: gopherbot

Change https://go.dev/cl/600855 mentions this issue: retrybuilds: rewrite tool to support LUCI