cmd/link/internal/ld: improve messages for testDWARF failures

Change-Id: I60af7a6477d1b25c43b311246ae4a79bf691460e
Reviewed-on: https://go-review.googlesource.com/c/go/+/171819Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/link/dwarf_test.go

@@ -93,11 +93,11 @@ func testDWARF(t *testing.T, buildmode string, expectDWARF bool, env ...string)
 					// Ensure Apple's tooling can parse our object for symbols.
 					out, err = exec.Command("symbols", exe).CombinedOutput()
 					if err != nil {
-						t.Fatal(err)
+						t.Fatalf("symbols %v: %v: %s", filepath.Base(exe), err, out)
 					} else {
 						if bytes.HasPrefix(out, []byte("Unable to find file")) {
 							// This failure will cause the App Store to reject our binaries.
-							t.Fatalf("/usr/bin/symbols %v: failed to parse file", filepath.Base(exe))
+							t.Fatalf("symbols %v: failed to parse file", filepath.Base(exe))
 						}
 					}
 				}