message: bump minimum cmake version to 3.8
diff: -cmake_minimum_required(VERSION 3.4)
  +cmake_minimum_required(VERSION 3.8)
  project(Alive2)
  @@ -15,15 +15,14 @@ if (MSVC)
  set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "/O2 /Oi /Zi")
  set(CMAKE_EXE_LINKER_FLAGS "/LTCG:INCREMENTAL ${CMAKE_EXE_LINKER_FLAGS}")
  else()
  - set(CMAKE_CXX_FLAGS "-std=c++17 -Wall -march=native -fPIC ${CMAKE_CXX_FLAGS}")
  + set(CMAKE_CXX_FLAGS "-Wall -march=native -fPIC ${CMAKE_CXX_FLAGS}")
  set(CMAKE_CXX_FLAGS_DEBUG "-Werror -g -Og")
  set(CMAKE_CXX_FLAGS_RELEASE "-O3 -DNDEBUG")
  set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELEASE} -g")
  endif()
  -# cmake doesn't support C++17 yet
  -#set(CMAKE_CXX_STANDARD 17)
  -#set(CMAKE_CXX_STANDARD_REQUIRED ON)
  +set(CMAKE_CXX_STANDARD 17)
  +set(CMAKE_CXX_STANDARD_REQUIRED ON)
  list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
  