test: drop ENTT_HAS_HEADER_VERSION

test/CMakeLists.txt

@@ -3,11 +3,6 @@
 include(FetchContent)
 include(CheckCXXSourceCompiles)
 
-check_cxx_source_compiles("
-    #include<version>
-    int main() { return 0; }
-" ENTT_HAS_HEADER_VERSION)
-
 set(THREADS_PREFER_PTHREAD_FLAG ON)
 find_package(Threads REQUIRED)
 
@@ -101,14 +96,6 @@ function(SETUP_TARGET TARGET_NAME)
             NOMINMAX
             ${ARGN}
     )
-
-    if(ENTT_HAS_HEADER_VERSION)
-        target_compile_definitions(
-            ${TARGET_NAME}
-            PRIVATE
-                ENTT_HAS_HEADER_VERSION
-        )
-    endif()
 endfunction()
 
 add_library(odr OBJECT odr.cpp)

test/common/tracked_memory_resource.hpp

@@ -1,7 +1,7 @@
 #ifndef ENTT_COMMON_TRACKED_MEMORY_RESOURCE_HPP
 #define ENTT_COMMON_TRACKED_MEMORY_RESOURCE_HPP
 
-#ifdef ENTT_HAS_HEADER_VERSION
+#if __has_include(<version>)
 #    include <version>
 #
 #    if defined(__cpp_lib_memory_resource) && __cpp_lib_memory_resource >= 201603L