Revert "Revert "Automated NDK API coverage used by Mainline modules build integration.""

This reverts commit 556b2ad7.

Original change-id: Ib1b2f0dd2f9ae85b1545c6cc5bb4c5bbdfac1c15

Reason for revert: Add excutable permission to the gen_ndk_backedby_apex.sh.

Test: TARGET_BUILD_APPS=com.android.adbd m dist apps_only

Change-Id: Ib587ba200cd7f2f61d478452b43c329d72b2de06