Fix llama runner on MacOS (#13869)

Summary:

Fixes two things:

- There's a compilation error when building the tests due to missing
header. Make sure it works via test_llama.sh
- rpath isn't set correctly on MacOS

Test Plan:

```
cmake --preset llm -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=cmake-out

cmake --build cmake-out -j16 --target install --config Release

cmake -DCMAKE_INSTALL_PREFIX=cmake-out \
	-DBUILD_TESTING=OFF \
	-DCMAKE_BUILD_TYPE=Release \
	-Bcmake-out/examples/models/llama \
	examples/models/llama

cmake --build cmake-out/examples/models/llama -j16 --config Release
```

Author: mergennachin

.ci/scripts/test_llama.sh

@@ -154,6 +154,7 @@ cmake_install_executorch_libraries() {
     echo "Installing libexecutorch.a, libextension_module.so, libportable_ops_lib.a"
     rm -rf cmake-out
     retry cmake --preset llm \
+        -DEXECUTORCH_BUILD_TESTS=ON \
         -DBUILD_TESTING=OFF \
         -DCMAKE_INSTALL_PREFIX=cmake-out \
         -DCMAKE_BUILD_TYPE="$CMAKE_BUILD_TYPE" \
@@ -170,6 +171,7 @@ cmake_build_llama_runner() {
     popd
     dir="examples/models/llama"
     retry cmake \
+        -DEXECUTORCH_BUILD_TESTS=ON \
         -DBUILD_TESTING=OFF \
         -DCMAKE_INSTALL_PREFIX=cmake-out \
         -DCMAKE_BUILD_TYPE="$CMAKE_BUILD_TYPE" \

examples/models/llama/CMakeLists.txt

@@ -220,7 +220,8 @@ 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 ${_common_compile_options})
 if(APPLE)
-  target_link_options(llama_main PRIVATE -Wl,-rpath,@executable_path)
+  target_link_options(llama_main PRIVATE -Wl,-rpath,@loader_path)
 elseif(UNIX)
   set_target_properties(llama_main PROPERTIES LINK_FLAGS "-Wl,-rpath='$ORIGIN'")
 endif()
+# Windows doesn't need rpath - DLLs are found via standard Windows search order

runtime/executor/test/method_test.cpp

@@ -8,6 +8,7 @@
 
 #include <cstdlib>
 #include <filesystem>
+#include <unordered_map>
 
 #include <executorch/extension/data_loader/file_data_loader.h>
 #include <executorch/extension/flat_tensor/flat_tensor_data_map.h>