cmake: Add BOOST_NO_CXX98_FUNCTION_BASE definition when needed

Author: hebasto

cmake/module/AddBoostIfNeeded.cmake

@@ -32,6 +32,28 @@ function(add_boost_if_needed)
     )
   endif()
 
+  # Prevent use of std::unary_function, which was removed in C++17,
+  # and will generate warnings with newer compilers for Boost
+  # older than 1.80.
+  # See: https://github.com/boostorg/config/pull/430.
+  include(CMakePushCheckState)
+  cmake_push_check_state(RESET)
+  set(CMAKE_REQUIRED_DEFINITIONS -DBOOST_NO_CXX98_FUNCTION_BASE)
+  set(CMAKE_REQUIRED_INCLUDES ${Boost_INCLUDE_DIR})
+  include(TryAppendCXXFlags)
+  set(CMAKE_REQUIRED_FLAGS ${working_compiler_werror_flag})
+  set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+  check_cxx_source_compiles("
+    #include <boost/config.hpp>
+    " NO_DIAGNOSTICS_BOOST_NO_CXX98_FUNCTION_BASE
+  )
+  cmake_pop_check_state()
+  if(NO_DIAGNOSTICS_BOOST_NO_CXX98_FUNCTION_BASE)
+    target_compile_definitions(Boost::headers INTERFACE
+      BOOST_NO_CXX98_FUNCTION_BASE
+    )
+  endif()
+
   if(BUILD_TESTS)
     include(CheckCXXSourceCompiles)
     set(CMAKE_REQUIRED_INCLUDES ${Boost_INCLUDE_DIR})