Only use compiler features if available

CMakeLists.txt

@@ -69,7 +69,13 @@ set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH}
 include(cxx14)
 include(CheckCXXCompilerFlag)
 
-set(FMT_REQUIRED_FEATURES cxx_auto_type cxx_variadic_templates)
+list(FIND CMAKE_CXX_COMPILE_FEATURES "cxx_variadic_templates" index)
+if (${index} GREATER -1)
+  # Use cxx_variadic_templates instead of more appropriate cxx_std_11 for
+  # compatibility with older CMake versions.
+  set(FMT_REQUIRED_FEATURES cxx_variadic_templates)
+endif ()
+message(STATUS "Required features: ${FMT_REQUIRED_FEATURES}")
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
   set(PEDANTIC_COMPILE_FLAGS -pedantic-errors -Wall -Wextra -pedantic