lineage: add soong bits for boardflags

Change-Id: If01db1eb6b1432a6c4d26d5c9701895ab4dc3ff5
diff --git a/build/soong/android/variable.go b/build/soong/android/variable.go
new file mode 100644
index 0000000..11569a3
--- /dev/null
+++ b/build/soong/android/variable.go
@@ -0,0 +1,6 @@
+package android
+type Product_variables struct {
+}
+
+type ProductVariables struct {
+}