Update prebuilt Clang to r349610b.

clang 8.0.9 (based on r349610b) from build 5331180.

Bug: http://b/122481018
Test: N/A
Change-Id: I21bb9f61c287ea9397cf66cc0941f267e3451740
(cherry picked from commit a59d17df840d203e477534a3312b36e2310712d0)