cmd/go: respect -n flag in 'go tool' command

src/cmd/go/internal/tool/tool.go

@@ -44,7 +44,7 @@ may be defined in the go.mod of the current module.
 With no arguments it prints the list of known tools.
 
 The -n flag causes tool to print the command that would be
-executed but not execute it.
+executed but not execute it. (the path to the executable shown may not actually exist.)
 
 The -modfile=file.mod build flag causes tool to use an alternate file
 instead of the go.mod in the module root directory.
@@ -302,6 +302,7 @@ func buildAndRunModtool(ctx context.Context, tool string, args []string) {
 	p.Internal.OmitDebug = true
 	p.Internal.ExeName = p.DefaultExecName()
 
+	cfg.BuildN = toolN
 	a1 := b.LinkAction(work.ModeBuild, work.ModeBuild, p)
 	a1.CacheExecutable = true
 	a := &work.Action{Mode: "go tool", Actor: work.ActorFunc(runBuiltTool), Args: args, Deps: []*work.Action{a1}}