Use uppercase OR when checking for system XNNPACK (pytorch#159527)

This PR fixes `cmake/Dependencies.cmake` to work when compiling with `USE_SYSTEM_XNNPACK=ON` by changing a lowercase `or` to an uppercase `OR`.

---

For a personal project, I was building pytorch with a customized build of XNNPACK. When trying to do so I encountered the following error:

```
CMake Error at cmake/Dependencies.cmake:566 (if):
  if given arguments:

    "NOT" "XNNPACK_LIBRARY" "or" "NOT" "microkernels-prod_LIBRARY"

  Unknown arguments specified
Call Stack (most recent call first):
  CMakeLists.txt:868 (include)
```

Upon making the change in this PR (changing `or` to `OR`), the process continued as expected.
Pull Request resolved: pytorch#159527
Approved by: https://github.com/janeyx99

Author: benjaminhottell

cmake/Dependencies.cmake

@@ -576,7 +576,7 @@ elseif(NOT TARGET XNNPACK AND USE_SYSTEM_XNNPACK)
   find_library(microkernels-prod_LIBRARY microkernels-prod)
   set_property(TARGET XNNPACK PROPERTY IMPORTED_LOCATION "${XNNPACK_LIBRARY}")
   set_property(TARGET microkernels-prod PROPERTY IMPORTED_LOCATION "${microkernels-prod_LIBRARY}")
-  if(NOT XNNPACK_LIBRARY or NOT microkernels-prod_LIBRARY)
+  if(NOT XNNPACK_LIBRARY OR NOT microkernels-prod_LIBRARY)
     message(FATAL_ERROR "Cannot find XNNPACK")
   endif()
   message("-- Found XNNPACK: ${XNNPACK_LIBRARY}")