[Windows] misc fixes to enable Windows build (#9198)

Summary:
## Context

Implement some small miscellaneous fixes to enable installing ExecuTorch
on Windows. Currently, the optimized kernels cannot be built
successfully but the installation works in custom ops are not built.

## Installation

```powershell
cd executorch

# Need to disable building custom kernels; there are a bunch of build errors
$env:EXECUTORCH_BUILD_KERNELS_CUSTOM_AOT=0
# For some reason need to explicitly enable tensor extension otherwise I see a linker error
$env:CMAKE_ARGS="-DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON"

python install_executorch.py

# Unset if you want
Remove-Item Env:\EXECUTORCH_BUILD_KERNELS_CUSTOM_AOT
Remove-Item Env:\CMAKE_ARGS
```

## Testing

I am able to follow the [Getting Started
tutorial](https://pytorch.org/executorch/stable/getting-started-setup.html#run-your-program)
successfully.

## Outstanding Build Issues

Currently, with CMake I can successfully build with the following
settings:

```
del -Recurse -Force cmake-out; `
  cmake . `
  -DCMAKE_INSTALL_PREFIX=cmake-out `
  -DPYTHON_EXECUTABLE=C:\\Users\\ssjia\\AppData\\Local\\miniconda3\\python.exe `
  -DCMAKE_PREFIX_PATH=C:\\Users\\ssjia\\AppData\\Local\\miniconda3\\Lib\\site-packages `
  -DCMAKE_BUILD_TYPE=Release `
  -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON `
  -DEXECUTORCH_BUILD_PYBIND=ON `
  -DEXECUTORCH_BUILD_XNNPACK=ON `
  -DEXECUTORCH_BUILD_KERNELS_QUANTIZED_AOT=ON `
  -DEXECUTORCH_BUILD_KERNELS_CUSTOM_AOT=ON `
  -DEXECUTORCH_BUILD_KERNELS_CUSTOM=OFF `
  -T ClangCL `
  -Bcmake-out; `
  cmake --build cmake-out -j64 --target install
```

If I switch `EXECUTORCH_BUILD_KERNELS_CUSTOM` to `ON`, then the build
fails. The primary offenders appear to be the `gelu`. The implementation
includes a header from ATen which is causing the majority of the errors.