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

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

Change-Id: I1a8ac13966116c997c2a3be923f3c3ba6fbe2258
diff --git a/androidmk/cmd/androidmk/androidmk.go b/androidmk/cmd/androidmk/androidmk.go
index 71e69ac..03888fe 100644
--- a/androidmk/cmd/androidmk/androidmk.go
+++ b/androidmk/cmd/androidmk/androidmk.go
@@ -166,6 +166,8 @@
 				file.errorf(directive, "unsupported directive")
 				continue
 			}
+		} else {
+			file.errorf(t, "unsupported line")
 		}
 	}