message: ranges_flags: /external:I is overkill
diff: @@ -22,7 +22,7 @@ if (RANGES_CXX_COMPILER_CLANGCL OR RANGES_CXX_COMPILER_MSVC)
  ranges_append_flag(RANGES_HAS_CXXSTDCOLON "/std:c++${RANGES_CXX_STD}")
  set(RANGES_STD_FLAG "/std:c++${RANGES_CXX_STD}")
  # Enable strict mode
  - ranges_append_flag(RANGES_HAS_PERMISSIVEMINUS "-permissive-")
  + ranges_append_flag(RANGES_HAS_PERMISSIVEMINUS "/permissive-")
  if (RANGES_CXX_COMPILER_CLANGCL)
  ranges_append_flag(RANGES_HAS_FNO_MS_COMPATIBIILITY "-fno-ms-compatibility")
  ranges_append_flag(RANGES_HAS_FNO_DELAYED_TEMPLATE_PARSING "-fno-delayed-template-parsing")
  @@ -53,7 +53,7 @@ endif()
  # Deep integration support
  if (RANGES_DEEP_STL_INTEGRATION)
  if (RANGES_CXX_COMPILER_MSVC)
  - add_compile_options(/external:I "${PROJECT_SOURCE_DIR}/include/std")
  + add_compile_options(/I "${PROJECT_SOURCE_DIR}/include/std")
  else()
  add_compile_options(-isystem "${PROJECT_SOURCE_DIR}/include/std")
  endif()
  