message: roll back some cmake changes to hopefully make travis and appveyor happy
diff: @@ -13,15 +13,15 @@ project(Range-v3 CXX)
  list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
  set(CMAKE_EXPORT_COMPILE_COMMANDS ON) # Export compilation data-base
  -include(TestHeaders)
  -include(ranges_options)
  -include(ranges_env)
  -include(ranges_flags)
  -include(CTest)
  +# include(TestHeaders)
  +# include(ranges_options)
  +# include(ranges_env)
  +# include(ranges_flags)
  +# include(CTest)
  -enable_testing()
  +# enable_testing()
  -add_definitions(-D_GLIBCXX20_CONSTEXPR=)
  +# add_definitions(-D_GLIBCXX20_CONSTEXPR=)
  add_library(meta INTERFACE)
  target_include_directories(meta INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/>)
  @@ -38,6 +38,12 @@ target_include_directories(range-v3 INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_
  target_include_directories(range-v3 SYSTEM INTERFACE $<INSTALL_INTERFACE:$<INSTALL_PREFIX>/include>)
  target_link_libraries(range-v3 INTERFACE concepts meta)
  +include(TestHeaders)
  +include(ranges_options)
  +include(ranges_env)
  +include(ranges_flags)
  +include(CTest)
  +
  # Test for <thread>
  try_compile(RANGE_V3_TRY_THREAD ${CMAKE_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/thread_test_code.cpp)
  