enable boost concepts

CMakeLists.txt

@@ -279,8 +279,6 @@ endif()
 # Configure C++ standard
 # ===========================
 
-# boost asio's concept usage doesn't play nicely with some compilers yet.
-add_definitions(-DBOOST_ASIO_DISABLE_CONCEPTS)
 if (MSVC)
     add_compile_options($<$<COMPILE_LANGUAGE:CXX>:/std:c++20>)