explicitly linking to Darwin in CMake file, necessary to install on Mac OS X

cmake/CoreHelpers.cmake

@@ -70,7 +70,8 @@ function(core_add_library)
     set_target_properties(${target} PROPERTIES OUTPUT_NAME ${PROJECT_NAME}${modname})
     target_include_directories(${target} PUBLIC  "interface")
     target_include_directories(${target} PRIVATE "src")
-    target_link_libraries(${target} PUBLIC ${ARG_DEPENDS})
+    target_link_libraries(${target} PUBLIC Darwin::Darwin ${ARG_DEPENDS})
+
     install(TARGETS ${target}
             RUNTIME DESTINATION "${CMAKE_INSTALL_LIBDIR}")