androidmk: print unsupported $(call) and $(eval) lines

Unsupported top level lines were getting silently dropped, print
an unsupported translation error instead.

Change-Id: I1a8ac13966116c997c2a3be923f3c3ba6fbe2258

androidmk/cmd/androidmk/androidmk.go

@@ -166,6 +166,8 @@ func main() {
 				file.errorf(directive, "unsupported directive")
 				continue
 			}
+		} else {
+			file.errorf(t, "unsupported line")
 		}
 	}