Switch to clang-3688880.

Bug: http://b/31532493
Test: Manual validation.
Change-Id: I7c415a1008c368a4b65bac2b5cd3ded3f4bb9de0
diff --git a/core/clang/versions.mk b/core/clang/versions.mk
index 711e5a4..abed69b 100644
--- a/core/clang/versions.mk
+++ b/core/clang/versions.mk
@@ -1,4 +1,4 @@
 ## Clang/LLVM release versions.
 
-LLVM_PREBUILTS_VERSION ?= clang-3289846
+LLVM_PREBUILTS_VERSION ?= clang-3688880
 LLVM_PREBUILTS_BASE ?= prebuilts/clang/host