"Update" clang.

Chromium ended up reverting their most recent roll, so match that.

Change-Id: I54b6351591d9169651f450ec3e800c7c9c28735c
Reviewed-on: https://boringssl-review.googlesource.com/30806
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

util/bot/update_clang.py

diff --git a/util/bot/update_clang.py b/util/bot/update_clang.py
index ac7f945..0a91189 100644
--- a/util/bot/update_clang.py
+++ b/util/bot/update_clang.py
@@ -19,7 +19,7 @@
 # CLANG_REVISION and CLANG_SUB_REVISION determine the build of clang
 # to use. These should be synced with tools/clang/scripts/update.py in
 # Chromium.
-CLANG_REVISION = '338452'
+CLANG_REVISION = '337439'
 CLANG_SUB_REVISION=1
 
 PACKAGE_VERSION = "%s-%s" % (CLANG_REVISION, CLANG_SUB_REVISION)