revert(ascend-custom): drop pip install build-isolation accommodations

The `--unset=PYTHONPATH` in `add_custom_command` and the `CMAKE_EXE`
forwarding in `build.sh` existed solely so `pip install -e .[dev]`
(default build-isolation) could drive `build.sh` on Ascend.  Drop both
and require `--no-build-isolation` for Ascend installs — the official
workflow.  The `add_custom_command` driver, `BUILD_ASCEND_CUSTOM`
gate, and `detect_soc.cmake` helper are unrelated to build isolation
and stay.

Author: zhangyue

src/CMakeLists.txt

@@ -269,26 +269,24 @@ if(WITH_ASCEND)
             "${CMAKE_CURRENT_SOURCE_DIR}/ascend/custom/build.sh")
 
         # Scrub env inherited from the outer `scikit-build-core` invocation
-        # before handing control to `build.sh`:
-        #  * `CMAKE_GENERATOR` / `CMAKE_EXPORT_COMPILE_COMMANDS` leaking
-        #    into the inner `cmake` change the path format passed to
-        #    `ninja`'s `_host_cpp` rule and re-trigger the `CANN`
-        #    `extract_host_stub.py` `KeyError` (`/./workspace/...`) that
-        #    standalone `build.sh` avoids.
-        #  * `PYTHONPATH` from `pip`'s build-isolation overlay makes the
-        #    child `python3` skip the system `site-packages` — child
-        #    `cmake` modules that `import torch` (`config_envs.cmake`)
-        #    then fail with `ModuleNotFoundError` even though `torch` is
-        #    installed.
+        # before handing control to `build.sh`: `CMAKE_GENERATOR` /
+        # `CMAKE_EXPORT_COMPILE_COMMANDS` leaking into the inner `cmake`
+        # change the path format passed to `ninja`'s `_host_cpp` rule and
+        # re-trigger the `CANN` `extract_host_stub.py` `KeyError`
+        # (`/./workspace/...`) that standalone `build.sh` avoids.
+        #
+        # `pip install` MUST be invoked with `--no-build-isolation` on
+        # Ascend; otherwise pip's build-isolation overlay shadows system
+        # `torch` (via `PYTHONPATH`) and the inner `cmake`'s
+        # `import torch` in `config_envs.cmake` fails with
+        # `ModuleNotFoundError`.
         add_custom_command(
             OUTPUT ${_custom_lib}
             COMMAND ${CMAKE_COMMAND} -E env
                     --unset=CMAKE_GENERATOR
                     --unset=CMAKE_EXPORT_COMPILE_COMMANDS
                     --unset=CMAKE_BUILD_PARALLEL_LEVEL
-                    --unset=PYTHONPATH
                     "BUILD_DIR=${_custom_build_dir}"
-                    "CMAKE_EXE=${CMAKE_COMMAND}"
                     bash ${CMAKE_CURRENT_SOURCE_DIR}/ascend/custom/build.sh ${SOC_VERSION}
             WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/ascend/custom
             DEPENDS ${_custom_srcs}

src/ascend/custom/build.sh

@@ -9,13 +9,6 @@ set -e
 
 SOC_VERSION="${1:-Ascend910_9382}"
 
-# Use the same `cmake` the caller resolved (default: first `cmake` on
-# PATH).  The outer `src/CMakeLists.txt` forwards `${CMAKE_COMMAND}`
-# via `CMAKE_EXE` so the child build doesn't accidentally pick up the
-# PyPI `cmake` shim whose Python package only exists in `pip`'s
-# build-isolation overlay.
-CMAKE_EXE="${CMAKE_EXE:-cmake}"
-
 # Detect CANN toolkit path.
 _CANN_TOOLKIT_INSTALL_PATH=$(grep "Toolkit_InstallPath" /etc/Ascend/ascend_cann_install.info | awk -F'=' '{print $2}')
 source "${_CANN_TOOLKIT_INSTALL_PATH}/set_env.sh"
@@ -32,14 +25,14 @@ OUTPUT_DIR="${BUILD_DIR}/output"
 rm -rf "${BUILD_DIR}"
 mkdir -p "${BUILD_DIR}" "${OUTPUT_DIR}"
 
-"${CMAKE_EXE}" \
+cmake \
     -DASCEND_HOME_PATH="${ASCEND_HOME_PATH}" \
     -DASCEND_INCLUDE_DIR="${ASCEND_INCLUDE_DIR}" \
     -DSOC_VERSION="${SOC_VERSION}" \
     -DCMAKE_LIBRARY_OUTPUT_DIRECTORY="${OUTPUT_DIR}" \
     -B "${BUILD_DIR}" \
     -S "${SCRIPT_DIR}"
 
-"${CMAKE_EXE}" --build "${BUILD_DIR}" -j 16
+cmake --build "${BUILD_DIR}" -j 16
 
 echo "Build complete. Output: ${OUTPUT_DIR}"