message: only look for C++ compiler with CMake
  Problem:
  For unclear reason, only the C compiler fails CMake's compiler tests.
  But since doctest is a header-only C++ library, we can just allow it
  to be built with miniconda3's toolchain on MacOSX under SDK>=10.14.
  This change can also reduce compiler testing time.
diff: @@ -5,7 +5,7 @@ cmake_minimum_required(VERSION 3.0)
  ################################################################################
  file(READ ${CMAKE_CURRENT_SOURCE_DIR}/scripts/version.txt ver)
  -project(doctest VERSION ${ver})
  +project(doctest VERSION ${ver} LANGUAGES CXX)
  option(DOCTEST_WITH_TESTS "Build tests/examples" ON)
  option(DOCTEST_WITH_MAIN_IN_STATIC_LIB "Build a static lib (cmake target) with a default main entry point" ON)
  