cmd/go: pass os.Args[0] to mod tools

Fixes #70509

Change-Id: I62952c0ac5de456742b7bee3552a0d90238bfde5
Reviewed-on: https://go-review.googlesource.com/c/go/+/631075
Reviewed-by: Michael Matloob <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>

Author: ConradIrwin

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

@@ -305,7 +305,7 @@ func runBuiltTool(b *work.Builder, ctx context.Context, a *work.Action) error {
 
 	toolCmd := &exec.Cmd{
 		Path:   cmdline[0],
-		Args:   cmdline[1:],
+		Args:   cmdline,
 		Stdin:  os.Stdin,
 		Stdout: os.Stdout,
 		Stderr: os.Stderr,

src/cmd/go/testdata/script/tool_exename.txt

@@ -12,6 +12,12 @@ go tool bar
 stdout 'my name is: bar'$GOEXE
 ! stdout 'a.out'
 
+# Third run: with arguments
+# https://go.dev/issue/70509
+go tool bar --baz
+stdout 'my name is: bar'$GOEXE
+! stdout 'a.out'
+
 -- go.mod --
 module example.com/foo