to enable other subprojects to use their own instance of
Blueprint in other directories.
Files named Android.bp are still autodetected throughout the
tree like previously.
Bug: 64363847
Test: mkdir -p subdir \
&& echo "syntax error" > Blueprints \
&& m -j nothing
Test: build/soong/scripts/diff_build_graphs.sh \
--products=aosp_arm \
'build/soong:work^' 'build/soong:work'
Change-Id: I8199f12b68dc1699bf44682b86169def37b53a5e