These prebuilts are for the RenderScript runtime libraries. They are target-device-agnostic, and only differ or 32-bit vs. 64-bit usage. They are generated and copied from the below listed Build ID, although local builds are bit-identical. To regenerate these files, one would need to check out a tree based on that manifest and make further changes to it in order to produce different bitcode files.
http://b/301495450 tracks the switchover to prebuilts, although it is only visible to Googlers.
system/lib
and system/lib64
.system/lib
and system/lib64
.Bug: http://b/301495450 Test: mm in frameworks/rs/driver/runtime with no Clang