test/fixedbugs: add mipsx case to issue11656

Change-Id: Ifcbd2ea19fc7fa832cd88aa857a5704c32eb4765
Reviewed-on: https://go-review.googlesource.com/34511Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue11656.go

@@ -61,9 +61,9 @@ func f(n int) {
 		binary.BigEndian.PutUint32(ill, 0x7fe00008) // trap
 	case "ppc64le":
 		binary.LittleEndian.PutUint32(ill, 0x7fe00008) // trap
-	case "mips64":
+	case "mips", "mips64":
 		binary.BigEndian.PutUint32(ill, 0x00000034) // trap
-	case "mips64le":
+	case "mipsle", "mips64le":
 		binary.LittleEndian.PutUint32(ill, 0x00000034) // trap
 	case "s390x":
 		binary.BigEndian.PutUint32(ill, 0) // undefined instruction