Require c++17 for xtl testing

Author: serge-sans-paille

test/CMakeLists.txt

@@ -54,11 +54,11 @@ if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU"
         # Users may override the c++ standard:
         if(NOT DEFINED CMAKE_CXX_STANDARD OR "${CMAKE_CXX_STANDARD}" STREQUAL "")
             if (ENABLE_XTL_COMPLEX)
-                CHECK_CXX_COMPILER_FLAG("-std=c++14" HAS_CPP14_FLAG)
-                if (NOT HAS_CPP14_FLAG)
-                    message(FATAL_ERROR "Unsupported compiler -- xsimd requires C++14 support when xtl complex support is enabled")
+                CHECK_CXX_COMPILER_FLAG("-std=c++17" HAS_CPP17_FLAG)
+                if (NOT HAS_CPP17_FLAG)
+                    message(FATAL_ERROR "Unsupported compiler -- xsimd requires C++17 support when xtl complex support is enabled")
                 endif()
-                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
+                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")
             else()
                 CHECK_CXX_COMPILER_FLAG("-std=c++11" HAS_CPP11_FLAG)
                 if (NOT HAS_CPP11_FLAG)