Minor fix for cmake (#19552)

### Minor fix for cmake

When build on Linux, get a warning saying "
CMake Warning at CMakeLists.txt:1603 (message):
  MPI and NCCL disabled on Win build.
"

This message is not correct. So have such a fix to avoid any
misunderstanding from users.


![image](https://github.com/microsoft/onnxruntime/assets/10530022/848c2d77-a538-4e31-8e0d-4b539233e515)




### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

cmake/CMakeLists.txt

@@ -1600,7 +1600,7 @@ if (UNIX AND onnxruntime_USE_NCCL)
 else()
   set(onnxruntime_USE_NCCL OFF)
   set(onnxruntime_USE_MPI OFF)
-message( WARNING "MPI and NCCL disabled on Win build." )
+  message( WARNING "MPI and NCCL are disabled because build is on Windows or USE_NCCL is set to OFF." )
 endif()
 
 if (onnxruntime_USE_MPI)