[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 9e72d3e [ValueTracking] Use KnownBits::countMaxLeadingZeros/countMaxTrailingZeros to make code more readable. NFC
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   9e72d3e..849c605  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 849c60541b630ddf8cabf9179fa771b3f4207ec8.
CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.13.4 or higher is required.  You are running version 3.7.1


-- Configuring incomplete, errors occurred!