cmd/go: pass signals forward during "go tool"

This way, if a SIGINT is sent to the go command,
it is forwarded on to the underlying tool.

Otherwise trying to use os.Process.Signal to kill
"go tool compile" only kills the "go tool" not the "compile".

Change-Id: Iac7cd4f06096469f5e76164df813a379c0da3822
Reviewed-on: https://go-review.googlesource.com/c/go/+/282312
Trust: Russ Cox <[email protected]>
Run-TryBot: Russ Cox <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>

Author: rsc

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

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"os/signal"
 	"sort"
 	"strings"
 
@@ -85,7 +86,19 @@ func runTool(ctx context.Context, cmd *base.Command, args []string) {
 		Stdout: os.Stdout,
 		Stderr: os.Stderr,
 	}
-	err := toolCmd.Run()
+	err := toolCmd.Start()
+	if err == nil {
+		c := make(chan os.Signal, 100)
+		signal.Notify(c)
+		go func() {
+			for sig := range c {
+				toolCmd.Process.Signal(sig)
+			}
+		}()
+		err = toolCmd.Wait()
+		signal.Stop(c)
+		close(c)
+	}
 	if err != nil {
 		// Only print about the exit status if the command
 		// didn't even run (not an ExitError) or it didn't exit cleanly