Force ART modules to be built from source here, regardless of default.

When we start switching vanilla platform builds to use ART prebuilts,
this script should still build from sources.

Test: TH
Bug: 172480615
Change-Id: I04cb61b484855d22f22fd9b82f6abb30eb5665c3
diff --git a/scripts/build-mainline-modules.sh b/scripts/build-mainline-modules.sh
index ea62af4..b8485ea 100755
--- a/scripts/build-mainline-modules.sh
+++ b/scripts/build-mainline-modules.sh
@@ -61,6 +61,9 @@
   esac
 }
 
+# Make sure this build builds from source, regardless of the default.
+export SOONG_CONFIG_art_module_source_build=true
+
 OUT_DIR=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT= get_build_var OUT_DIR)
 DIST_DIR=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT= get_build_var DIST_DIR)