Find portable_lib.so in pip package during cmake build (#5961)

Summary:
* Rename `_portable_lib.cpython-3.<distribution info>.so` to `_portable_lib.so` so it can be found by CMake `find_library()`. This can be achieved by setting `SETUPTOOLS_EXT_SUFFIX`.
* Since `executorch-config.cmake` is also being used to find installed libraries such as `executorch.a`, `xnnpack_backend.a`, add a condition to tell if `executorch-config.cmake` is being used in cmake-out or site-packages.

Pull Request resolved: #5961

Reviewed By: metascroy

Differential Revision: D64014291

Pulled By: larryliu0820

fbshipit-source-id: 2757f2883d3f836e9efd45676f792c12f742e63d

Author: larryliu0820

build/packaging/env_var_script_linux.sh

@@ -11,6 +11,10 @@
 # Enable pybindings so that users can execute ExecuTorch programs from python.
 export EXECUTORCH_BUILD_PYBIND=1
 
+# Override extension suffix to be ".so", skipping package info such as
+# "cpython-311-x86_64-linux-gnu"
+export SETUPTOOLS_EXT_SUFFIX=".so"
+
 # Ensure that CMAKE_ARGS is defined before referencing it. Defaults to empty
 # if not defined.
 export CMAKE_ARGS="${CMAKE_ARGS:-}"

build/packaging/env_var_script_m1.sh

@@ -11,6 +11,10 @@
 # Enable pybindings so that users can execute ExecuTorch programs from python.
 export EXECUTORCH_BUILD_PYBIND=1
 
+# Override extension suffix to be ".so", skipping package info such as
+# "cpython-311-darwin"
+export SETUPTOOLS_EXT_SUFFIX=".so"
+
 # Ensure that CMAKE_ARGS is defined before referencing it. Defaults to empty
 # if not defined.
 export CMAKE_ARGS="${CMAKE_ARGS:-}"

setup.py

@@ -423,6 +423,11 @@ def run(self):
                 "devtools/bundled_program/schema/scalar_type.fbs",
                 "devtools/bundled_program/serialize/scalar_type.fbs",
             ),
+            # Install executorch-config.cmake to the root of the package.
+            (
+                "build/executorch-config.cmake",
+                "executorch-config.cmake",
+            ),
         ]
         for src, dst in src_to_dst:
             dst = os.path.join(dst_root, dst)