Use compile features cxx_auto_type cxx_variadic_templates instead of cxx_std_11

CMakeLists.txt

@@ -66,6 +66,8 @@ set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH}
 include(cxx14)
 include(CheckCXXCompilerFlag)
 
+set(FMT_REQUIRED_FEATURES cxx_auto_type cxx_variadic_templates)
+
 if (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
   set(PEDANTIC_COMPILE_FLAGS -pedantic-errors -Wall -Wextra -pedantic
       -Wold-style-cast -Wundef
@@ -158,10 +160,7 @@ if (FMT_PEDANTIC)
   target_compile_options(fmt PRIVATE ${PEDANTIC_COMPILE_FLAGS})
 endif ()
 
-if (NOT ${CMAKE_VERSION} VERSION_LESS 3.8)
-  target_compile_features(fmt INTERFACE cxx_std_11)
-endif ()
-
+target_compile_features(fmt INTERFACE ${FMT_REQUIRED_FEATURES})
 
 target_include_directories(fmt PUBLIC
   $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
@@ -185,9 +184,7 @@ add_library(fmt::fmt-header-only ALIAS fmt-header-only)
 
 target_compile_definitions(fmt-header-only INTERFACE FMT_HEADER_ONLY=1)
 
-if (NOT ${CMAKE_VERSION} VERSION_LESS 3.8)
-  target_compile_features(fmt-header-only INTERFACE cxx_std_11)
-endif ()
+target_compile_features(fmt-header-only INTERFACE ${FMT_REQUIRED_FEATURES})
 
 target_include_directories(fmt-header-only INTERFACE
   $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>