Arrange so that onnx-optimizer uses our own ONNX build, and links against the
shared libraries of ONNX.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 00633856..76a73853 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,8 +27,6 @@ if(NOT ONNX_OPT_USE_SYSTEM_PROTOBUF)
 endif()
 
 
-set(ONNX_ROOT ${PROJECT_SOURCE_DIR}/third_party/onnx)
-add_subdirectory_if_no_target(${ONNX_ROOT} ${ONNX_TARGET_NAME})
 
 file(READ "${PROJECT_SOURCE_DIR}/VERSION_NUMBER" ONNX_OPTIMIZER_VERSION)
 string(STRIP "${ONNX_OPTIMIZER_VERSION}" ONNX_OPTIMIZER_VERSION)
@@ -41,14 +39,14 @@ file(GLOB onnx_opt_srcs "onnxoptimizer/*.cc"
 list(REMOVE_ITEM onnx_opt_srcs "${PROJECT_SOURCE_DIR}/onnxoptimizer/cpp2py_export.cc")
 
 onnxopt_add_library(onnx_optimizer ${onnx_opt_srcs})
-target_link_libraries(onnx_optimizer PUBLIC ${ONNX_TARGET_NAME})
+target_link_libraries(onnx_optimizer PUBLIC ${ONNX_TARGET_NAME} onnx_proto)
 target_include_directories(onnx_optimizer PUBLIC
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>
     $<INSTALL_INTERFACE:include>
     )
 
 onnxopt_add_executable(onnx_optimizer_exec examples/onnx_optimizer_exec.cpp)
-target_link_libraries(onnx_optimizer_exec onnx_optimizer)
+target_link_libraries(onnx_optimizer_exec onnx_optimizer onnx_proto)
 
 
 file(GLOB onnx_opt_c_api_srcs "onnxoptimizer/c_api/*.cc"
@@ -116,7 +114,8 @@ if(BUILD_ONNX_PYTHON)
                           PRIVATE "-Wl,--whole-archive" $<TARGET_FILE:onnx_optimizer>
                                   "-Wl,--no-whole-archive")
     set_target_properties(onnx_opt_cpp2py_export
-                          PROPERTIES LINK_FLAGS "-Wl,--exclude-libs,ALL")
+                          PROPERTIES LINK_FLAGS "-Wl,--exclude-libs,ALL,-rpath=${CMAKE_INSTALL_PREFIX}/lib")
+
   endif()
 
   target_link_libraries(onnx_opt_cpp2py_export PRIVATE onnx_optimizer)
diff --git a/cmake/utils.cmake b/cmake/utils.cmake
index 6cca9f36..8e39d5c4 100644
--- a/cmake/utils.cmake
+++ b/cmake/utils.cmake
@@ -1,4 +1,4 @@
-include(${PROJECT_SOURCE_DIR}/third_party/onnx/cmake/Utils.cmake)
+include(${ONNX_ROOT}/cmake/Utils.cmake)
 
 # Poor man's FetchContent
 function(add_subdirectory_if_no_target dir target)