[dev.power64] runtime: fix gcinfo_test on power64x

The GC info masks for slices and strings were changed in
commit caab29a25f68, but the reference masks used by
gcinfo_test for power64x hadn't caught up.  Now they're
identical to amd64, so this CL fixes this test by combining
the reference masks for these platforms.

LGTM=rsc
R=rsc, dave
CC=golang-codereviews
https://golang.org/cl/162620044

src/runtime/gcinfo_test.go

@@ -137,7 +137,7 @@ func infoBigStruct() []byte {
 			BitsScalar, BitsScalar, BitsScalar, BitsScalar, // t int; y uint16; u uint64
 			BitsPointer, BitsDead, // i string
 		}
-	case "amd64":
+	case "amd64", "power64", "power64le":
 		return []byte{
 			BitsPointer,                        // q *int
 			BitsScalar, BitsScalar, BitsScalar, // w byte; e [17]byte
@@ -153,12 +153,6 @@ func infoBigStruct() []byte {
 			BitsScalar, BitsScalar, BitsDead, BitsScalar, BitsScalar, // t int; y uint16; u uint64
 			BitsPointer, BitsDead, // i string
 		}
-	case "power64", "power64le":
-		return []byte{
-			BitsPointer, BitsScalar, BitsScalar, BitsScalar,
-			BitsMultiWord, BitsSlice, BitsScalar, BitsScalar,
-			BitsScalar, BitsScalar, BitsMultiWord, BitsString,
-		}
 	default:
 		panic("unknown arch")
 	}