Update prebuilt Clang to build 4639204.

Built from version 6.0.1
based on r316199.
Test: N/A
Exempt-From-Owner-Approval: my branch
Change-Id: I559dafbff4204a469eb3f13b33b735e7a4883bf3
(cherry picked from commit 13c69a71b23ec033192b41690e388a93cefe38f2)
1876 files changed