Bump minimal required CMake version

[lukaszstolarczuk]

Currently, it doesn't configure properly on cmake-3.5.0 with 2 errors:

-- Detecting CXX compile features - done
-- Found Git: /usr/bin/git (found version "2.43.0")
CMake Error at CMakeLists.txt:51 (include):
  include could not find load file:

    FetchContent

-- Performing Test COMPILER_SUPPORTS_CXX14
-- Performing Test COMPILER_SUPPORTS_CXX14 - Success
CMake Error at source/layers/validation/CMakeLists.txt:39 (install):
  install TARGETS given unknown argument "NAMELINK_COMPONENT".

CMake Error at source/layers/tracing/CMakeLists.txt:51 (install):
  install TARGETS given unknown argument "NAMELINK_COMPONENT".

-- Looking for pthread.h
-- Looking for pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - found
-- Found Threads: TRUE
CMake Error at source/CMakeLists.txt:51 (install):
  install TARGETS given unknown argument "NAMELINK_COMPONENT".

-- Configuring incomplete, errors occurred!

The minimal version required for failing features are:

• 3.11 for https://cmake.org/cmake/help/latest/module/FetchContent.html
• 3.12 for https://cmake.org/cmake/help/latest/command/install.html (NAMELINK_COMPONENT )

I also double-checked this with a tool: https://github.com/nlohmann/cmake_min_version :

@luke   venv  ~/repos/cmake_min_version: python cmake_min_version.py ~/repos/luke/level-zero/
Found 9 CMake binaries from directory tools in 0.27 seconds

[  0%] CMake 3.9.0  ✘ error
       CMakeLists.txt:51 (include)
[ 25%] CMake 3.11.0 ✘ error
       source/layers/validation/CMakeLists.txt:39 (install)
[ 50%] CMake 3.12.0 ✔ works
[100%] Minimal working version: CMake 3.12.0

cmake_minimum_required(VERSION 3.12.0)