[AIX] Build fix for using system installed protobuf/onnx (microsoft#2…

…2272)

### Description
To fix the build issues for AIX OS while using system installed
protobuf/onnx.

### Motivation and Context
Code changes in this PR contains:

1. Fix for below compilation issue.
```
collect2: fatal error: library liblibprotobuf-lite not found
compilation terminated.
```
2.  Adding onnx library into dependency list for test applicaitons.

cmake/onnxruntime_unittests.cmake

@@ -1343,7 +1343,7 @@ if (NOT onnxruntime_ENABLE_TRAINING_TORCH_INTEROP)
     endif()
 
     if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
-      list(APPEND onnxruntime_shared_lib_test_LIBS onnxruntime_graph onnxruntime_session onnxruntime_providers onnxruntime_framework onnxruntime_util onnxruntime_mlas onnxruntime_optimizer onnxruntime_flatbuffers iconv re2)
+      list(APPEND onnxruntime_shared_lib_test_LIBS onnxruntime_graph onnxruntime_session onnxruntime_providers onnxruntime_framework onnxruntime_util onnxruntime_mlas onnxruntime_optimizer onnxruntime_flatbuffers iconv re2 onnx)
     endif()
 
     AddTest(DYN
@@ -1646,7 +1646,7 @@ if (NOT CMAKE_SYSTEM_NAME STREQUAL "Emscripten")
       list(APPEND onnxruntime_customopregistration_test_LIBS ${TENSORRT_LIBRARY_INFER})
     endif()
     if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
-      list(APPEND onnxruntime_customopregistration_test_LIBS onnxruntime_graph onnxruntime_session onnxruntime_providers onnxruntime_framework onnxruntime_util onnxruntime_mlas onnxruntime_optimizer onnxruntime_flatbuffers iconv re2 libprotobuf-lite onnx_proto nsync_cpp)
+      list(APPEND onnxruntime_customopregistration_test_LIBS onnxruntime_graph onnxruntime_session onnxruntime_providers onnxruntime_framework onnxruntime_util onnxruntime_mlas onnxruntime_optimizer onnxruntime_flatbuffers iconv re2 ${PROTOBUF_LIB} onnx onnx_proto nsync_cpp)
     endif()
     AddTest(DYN
             TARGET onnxruntime_customopregistration_test
@@ -1765,7 +1765,7 @@ if (onnxruntime_BUILD_SHARED_LIB AND NOT CMAKE_SYSTEM_NAME STREQUAL "Emscripten"
 
   set(onnxruntime_logging_apis_test_LIBS onnxruntime_common onnxruntime_test_utils)
   if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
-    list(APPEND onnxruntime_logging_apis_test_LIBS onnxruntime_session onnxruntime_util onnxruntime_framework onnxruntime_common onnxruntime_graph  onnxruntime_providers onnxruntime_mlas onnxruntime_optimizer onnxruntime_flatbuffers iconv re2 libprotobuf-lite onnx_proto nsync_cpp)
+    list(APPEND onnxruntime_logging_apis_test_LIBS onnxruntime_session onnxruntime_util onnxruntime_framework onnxruntime_common onnxruntime_graph  onnxruntime_providers onnxruntime_mlas onnxruntime_optimizer onnxruntime_flatbuffers iconv re2 ${PROTOBUF_LIB} onnx onnx_proto nsync_cpp)
      endif()
 
   if(NOT WIN32)