Qualcomm AI Engine Direct - Fixed build error for llama runner on Mac (pytorch#13838)

As title. It appears that $ORIGIN doesn't exist as an environment
variable on Mac.

Author: shewu-quic

examples/models/llama/CMakeLists.txt

@@ -219,4 +219,6 @@ endif()
 target_include_directories(llama_main PUBLIC ${_common_include_directories})
 target_link_libraries(llama_main PUBLIC llama_runner ${link_libraries})
 target_compile_options(llama_main PUBLIC ${_common_compile_options})
-set_target_properties(llama_main PROPERTIES LINK_FLAGS "-Wl,-rpath='$ORIGIN'")
+if(NOT APPLE)
+  set_target_properties(llama_main PROPERTIES LINK_FLAGS "-Wl,-rpath='$ORIGIN'")
+endif()