Update clang tools to 4.0.

This includes clang-tidy-4.0 and clang-format-4.0.

Change-Id: I9c49002dee3c424e9745d68ba7dcfe10a858db12
diff --git a/tools/clang_format.py b/tools/clang_format.py
index 7351506..a0d000c 100755
--- a/tools/clang_format.py
+++ b/tools/clang_format.py
@@ -38,8 +38,8 @@
 import printer
 import util
 
-CLANG_FORMAT_VERSION_MAJOR = 3
-CLANG_FORMAT_VERSION_MINOR = 8
+CLANG_FORMAT_VERSION_MAJOR = 4
+CLANG_FORMAT_VERSION_MINOR = 0
 
 DEFAULT_CLANG_FORMAT = \
     'clang-format-{}.{}'.format(CLANG_FORMAT_VERSION_MAJOR,