cmd/compile: fix path for go tool in test

Fixes #23326

Change-Id: I6abc353ab004aadc6a4cbefbff3198f848640d7f
Reviewed-on: https://go-review.googlesource.com/87036
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/ssa_test.go

@@ -82,7 +82,7 @@ func runGenTest(t *testing.T, filename, tmpname string, ev ...string) {
 
 	stdout.Reset()
 	stderr.Reset()
-	cmd = exec.Command("go", "run", "-gcflags=-d=ssa/check/on", rungo)
+	cmd = exec.Command(gotool, "run", "-gcflags=-d=ssa/check/on", rungo)
 	cmd.Stdout = &stdout
 	cmd.Stderr = &stderr
 	cmd.Env = append(cmd.Env, ev...)