build: link boost modules as system libs

CMakeLists.txt

@@ -139,14 +139,24 @@ file(GLOB_RECURSE BOOST_URL_SOURCES CONFIGURE_DEPENDS src/*.cpp)
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR}/include/boost PREFIX "" FILES ${BOOST_URL_HEADERS})
 source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR}/src PREFIX "url" FILES ${BOOST_URL_SOURCES})
+
+function(target_link_as_system_libraries target visibility)
+    foreach(linked_target IN LISTS ARGN)
+        get_target_property(OTHER_TARGET_INCLUDE_DIRS ${linked_target} INTERFACE_INCLUDE_DIRECTORIES)
+        target_include_directories(${target} SYSTEM ${visibility} ${OTHER_TARGET_INCLUDE_DIRS})
+        target_link_libraries(${target} PRIVATE ${linked_target})
+    endforeach()
+endfunction()
+
+
 function(boost_url_setup_properties target)
     target_compile_features(${target} PUBLIC cxx_constexpr)
     target_compile_definitions(${target} PUBLIC BOOST_URL_NO_LIB=1)
     if (BOOST_URL_DISABLE_THREADS)
         target_compile_definitions(${target} PUBLIC BOOST_URL_DISABLE_THREADS=1)
     endif()
     target_include_directories(${target} PUBLIC "${PROJECT_SOURCE_DIR}/include")
-    target_link_libraries(${target} PUBLIC ${BOOST_URL_DEPENDENCIES})
+    target_link_as_system_libraries(${target} PUBLIC ${BOOST_URL_DEPENDENCIES})
     target_compile_definitions(${target} PUBLIC $<IF:$<BOOL:${BUILD_SHARED_LIBS}>,BOOST_URL_DYN_LINK=1,BOOST_URL_STATIC_LINK=1>)
     target_compile_definitions(${target} PRIVATE BOOST_URL_SOURCE)
     target_compile_options(${target} PUBLIC $<$<CXX_COMPILER_ID:MSVC>:/EHsc>)

test/Jamfile

@@ -21,6 +21,7 @@ project
     <toolset>gcc:<cxxflags>"-Wno-unused-but-set-variable"
     <toolset>gcc:<cxxflags>"-Wno-maybe-uninitialized"
     <toolset>clang:<cxxflags>"-Wno-unused-but-set-variable"
+    <toolset>clang:<cxxflags>"-Wno-unused-parameter"
     <toolset>gcc,<target-os>windows:<cxxflags>"-Wno-error=array-bounds"
 
     # Different typeinfos confuse ubsan