[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 63ba82e [X86] Use TargetConstant for immediates for VASTART_SAVE_XMM_REGS.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   63ba82e..180548c  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 180548c5c7848f82ceac5d6a3528a8cb14c20fed.
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!