Add pybind extension to the dll search path on Windows

Author: GregoryComer

extension/pybindings/portable_lib.py

@@ -13,6 +13,8 @@
     This API is experimental and subject to change without notice.
 """
 
+import os
+import sys
 import warnings as _warnings
 
 import executorch.exir._warnings as _exir_warnings
@@ -28,6 +30,13 @@
 # dependencies.
 import torch as _torch
 
+# Update the DLL search path on Windows. This is the recommended way to handle native
+# extensions.
+if sys.platform == "win32":
+    # The extension DLL should be in the same directory as this file.
+    pybindings_dir = os.path.dirname(__file__)
+    os.add_dll_directory(pybindings_dir)
+
 # Let users import everything from the C++ _portable_lib extension as if this
 # python file defined them. Although we could import these dynamically, it
 # wouldn't preserve the static type annotations.