Merge soong_{cc,rust}_prebuilt.mk

Much of soong_cc_prebuilt.mk is duplicated in soong_rust_prebuilt.mk.
This adds maintenance burden and increases the risk of bugs or
inconsistencies. Merge the two to simplify this.

Bug: N/A, clean-up
Test: m
Change-Id: I833fba94e299006b34f8e53d5519c6b19f684d39