fix: multi /pkg/<module> in dlv debugging

[wuhuua]

This issue is copied from my PR: cockroachdb/rules_go#18

When I try to debug cockroach with VSCode, I found some bugs when I try to set breakpoints.
VSCode tells me that some files cannot be found in dlv sources, even if I use this to substitute the path to package path:

  {
    "from": "${workspaceFolder}",
    "to": "github.com/cockroachdb/cockroach"
  }, 

One of the cases is /pkg/gossip/gossip.go
When using dlv as follows:

dlv exec ../_bazel/bin/pkg/cmd/cockroach/cockroach_/cockroach -- start --insecure --store=node1 --listen-addr=localhost:26257 --http-addr=localhost:8080 --join=localhost:26257,localhost:26258,localhost:26259

and then use sources command to list all sources. You can find its path like this:

github.com/cockroachdb/cockroach/pkg/gossip/pkg/gossip/gossip.go
The relpath pkg/gossip has been appended twice.

This problem is associated with one issue in cockroach:
#64379
You modified complilepkg.go as follows:

// We want the source files to show up (e.g. in stack traces) with the package
// path. We use -trimpath to replace the root path with the correct prefix
// of the package path.
root := abs(".")
relSrcPath, err := filepath.Rel(root, srcs.goSrcs[0].filename)
if err != nil {
  return err
}
rootPkgPath := filepath.Clean(strings.TrimSuffix(packagePath, filepath.Dir(relSrcPath)))
gcFlags = append(gcFlags, fmt.Sprintf("-trimpath=%s=>%s", root, rootPkgPath))

But when you debug bazel, you can get the command passed bazel looks like this:

bazel-out/k8-opt-exec-ST-13d3ddad9198/bin/external/go_sdk/builder_reset/builder compilepkg 
-sdk external/go_sdk -installsuffix linux_amd64 -tags bazel,gss,bazel,gss 
-src bazel-out/k8-dbg/bin/foo/foo_go_proto_/example.com/foo/foo.pb.go 
-src foo/foo.go -embedroot bazel-out/k8-dbg/bin -embedroot '' 
-embedlookupdir foo/foo_go_proto_/example.com/foo -embedlookupdir foo 
(serveral arcs)
-importpath heyhey -p example.com/foo -package_list bazel-out/k8-opt-exec-ST-13d3ddad9198/bin/external/go_sdk/packages.txt -o bazel-out/k8-dbg/bin/foo/foo.a -x bazel-out/k8-dbg/bin/foo/foo.x -gcflags '-N -l' -asmflags '')

The first src is the protobuf file and therefore srcs.goSrcs[0].filename is bazel-out/k8-dbg/bin/foo/foo_go_proto_/example.com/foo/foo.pb.go, but we are expecting the source file which is not generated.

so I modify this part as follows:

srcFullPath := srcs.goSrcs[0].filename
for _, goSrc := range srcs.goSrcs {
  if !strings.HasSuffix(goSrc.filename, ".pb.go") {
    srcFullPath = goSrc.filename
    break
  }
}
relSrcPath, err := filepath.Rel(root, srcFullPath)

Once srcs has source code which is not generated, we use its path.
Then problem is fixed, and we get its path in dlv as follows:
github.com/cockroachdb/cockroach/pkg/gossip/gossip.go

Jira issue: CRDB-36174

[blathers-crl]

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I have CC'd a few people who may be able to assist you:

• @rickystewart (commented on build: bazel-generated go binaries should include a synthetic prefix #64379)
• @RaduBerinde (commented on build: bazel-generated go binaries should include a synthetic prefix #64379)
• @cockroachdb/sql-queries (found keywords: import)
• @tbg (commented on Listen on random ports for tests instead of :8080 #18)

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[RaduBerinde]

CC @rickystewart