flounder: add aosp_flounder_64_only build

aosp_flounder_64_only is similar to aosp_flounder, but will only
start a 64-bit zygote and thus only support 64-bit apps.

Change-Id: I44da8931f3db97b0347dc8cddbbc36e54e518325
diff --git a/AndroidProducts.mk b/AndroidProducts.mk
index 9fa30d4..b58d0a7 100644
--- a/AndroidProducts.mk
+++ b/AndroidProducts.mk
@@ -18,3 +18,4 @@
 	$(LOCAL_DIR)/aosp_flounder.mk \
 	$(LOCAL_DIR)/aosp_flounder64.mk \
 	$(LOCAL_DIR)/aosp_flounder32.mk \
+	$(LOCAL_DIR)/aosp_flounder_64_only.mk