cmd/gorebuild: use expected executable name in TestStripDarwinSig

StripDarwinSig is a Fixer that expects to work only on Mach-O executable
files in GOROOT/bin and GOROOT/pkg/tool, and silently returns data as is
otherwise.

Fix TestStripDarwinSig to give StripDarwinSig an expected name such that
it does its job instead of doing nothing.

Change-Id: If48897965208c41a9e7ef049b3aafbfb26bfb385
Reviewed-on: https://go-review.googlesource.com/c/build/+/516296
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Russ Cox <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: dmitshur

cmd/gorebuild/pkg_darwin_test.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"runtime"
 	"sort"
 	"testing"
@@ -24,7 +25,7 @@ func TestStripDarwinSig(t *testing.T) {
 	}
 
 	var log Log
-	stripped := StripDarwinSig(&log, exe, data)
+	stripped := StripDarwinSig(&log, "/bin/"+filepath.Base(exe), data)
 	for _, m := range log.Messages {
 		t.Log(m.Text)
 	}