[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 7103878 Revert "[AArch64][AsmParser] Remove 'x31' alias for 'sp/xzr' register."
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   7103878..7706c30  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 7706c3022ead52d49cf455df7e7c289a485aa6ec.
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!