On OSX, add target library path to RPATH

CMakeLists.txt

@@ -218,6 +218,13 @@ set(MAGNUM_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/include/Magnum)
 set(MAGNUM_EXTERNAL_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/include/MagnumExternal)
 set(MAGNUM_PLUGINS_INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/include/MagnumPlugins)
 
+# If on OS X, add installation library directory to RPATH
+set(CMAKE_INSTALL_RPATH "${MAGNUM_LIBRARY_INSTALL_DIR}")
+set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)
+if(CORRADE_TARGET_APPLE)
+    set(CMAKE_MACOSX_RPATH 1)
+endif()
+
 # Separate install dirs for debug and release plugins
 set(MAGNUM_PLUGINS_DEBUG_INSTALL_DIR ${MAGNUM_LIBRARY_INSTALL_DIR}/magnum-d)
 set(MAGNUM_PLUGINS_RELEASE_INSTALL_DIR ${MAGNUM_LIBRARY_INSTALL_DIR}/magnum)