Publish the C++14 requirement through cmake interface

Author: serge-sans-paille

CMakeLists.txt

@@ -93,13 +93,11 @@ target_include_directories(xsimd INTERFACE
 OPTION(ENABLE_XTL_COMPLEX "enables support for xcomplex defined in xtl" OFF)
 OPTION(BUILD_TESTS "xsimd test suite" OFF)
 
+target_compile_features(xsimd INTERFACE cxx_std_14)
 if(ENABLE_XTL_COMPLEX)
     find_package(xtl 0.8.0 REQUIRED)
-    target_compile_features(xsimd INTERFACE cxx_std_14)
     target_compile_definitions(xsimd INTERFACE XSIMD_ENABLE_XTL_COMPLEX=1)
     target_link_libraries(xsimd INTERFACE xtl)
-else()
-    target_compile_features(xsimd INTERFACE cxx_std_11)
 endif()
 
 if(BUILD_TESTS)