Fix build.

Our continuous build uses a different TARGET_PRODUCT, and we want it to build
anyway, even if the result won't actually be useful.

This will be addressed later by moving this stuff out so every .apk gets this
done as it's built.

Change-Id: Iefa15615a5bcdd23e7eed99fb87bca86429fc109
diff --git a/Android.mk b/Android.mk
index 21b7ff5..6bbceb9 100644
--- a/Android.mk
+++ b/Android.mk
@@ -363,7 +363,7 @@
 
 else
 
-$(error do not know what jars to compile for $(TARGET_PRODUCT))
+$(warning do not know what jars to compile for $(TARGET_PRODUCT))
 
 endif