Update prebuilt Clang to r416183c1 (12.0.8).

clang 12.0.8 (based on r416183c1) from build 7714059.
Test: N/A

Change-Id: I7ccfccceb6283d8a777f30906e30295ef6bea21c
(cherry picked from commit 293bb9602e99f5d9b9ddc660545734656761c7df)