Fix infinite recursion when printing unrecognized linktype

Bug: N/A
Test: remove some cases from String() so that some linktypes go to the
default path. Then run m nothing. No infinite recursion. Error is
correctly shown.
PANIC=String method: unrecognized linktype: 5
Change-Id: I424755bc89871fc2144ff22d6391f57157cd434d

Change-Id: Ice791025dc50f44ffabd1050bafc5ea35023d32c

java/java.go

@@ -1038,7 +1038,7 @@ func (lt linkType) String() string {
 	case javaPlatform:
 		return "private API"
 	default:
-		panic(fmt.Errorf("unrecognized linktype: %v", lt))
+		panic(fmt.Errorf("unrecognized linktype: %d", lt))
 	}
 }