Adapt update_rs_prebuilts.sh to new SDK layout

The structure of SDK prebuilts has changed.  The files go into lib,
lib64 or bin subdirectories in prebuilts/sdk/tools/<OS>.  Adapt
update_rs_prebuilts.sh to this layout.  Currently, lib/ has just the
32-bit version of libc++.so

Change-Id: I11fc114ee0c888f2c54cb92db9e5084ca921fba5
(cherry picked from commit 9b0ec105175dc668cf4f373bdccc74f465fcb831)
1 file changed