MSVC static runtime library

[pierreguillot]

It would be great to be able to define the MSVC runtime library via CMAKE_MSVC_RUNTIME_LIBRARY (or the MSVC_RUNTIME_LIBRARY property). However, this feature has only been included in CMake 3.15. Would it be possible to set this version as the minimum? Or set the minimum version to 3.5 only if it is not yet defined?

if(NOT DEFINED CMAKE_MINIMUM_REQUIRED_VERSION)
  cmake_minimum_required(VERSION 3.5)
endif()

P.S. I can create a PR if necessary.