Bug 823906 - Last clang update on the 3.2 branch. r=rail.

Update the build scripts.

build/unix/build-clang/build-clang.py

@@ -3,7 +3,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-llvm_revision = "170377"
+llvm_revision = "170890"
 moz_version = "moz0"
 
 ##############################################