校验 MACA 构建环境

[ghangz]

该 PR 在构建前增加 MACA 关键依赖检查，提前暴露缺少编译器、运行库或路径配置的问题。

这个修改面向沐曦 GPU 适配场景中比较容易影响开发、构建或验证稳定性的环节，把原来需要人工排查的问题前移到工具链、运行前检查或基准脚本中处理。实现上保持对现有默认行为的兼容，只在检测到明确配置、输入或环境异常时给出更直接的诊断，避免引入额外运行依赖，也方便维护者独立审阅该分支。

已在沐曦算力环境中完成对应分支验证，验证记录包含真实运行日志、命令输出和失败路径检查，本地归档目录为：E:/Documents/muxi/测试报告/FlashMLA_real_maca_validation_20260608。提交分支：mengz/validate-maca-build-env，目标仓库：MetaX-MACA/FlashMLA。

[gemini-code-assist]

Code Review

This pull request introduces a structured way to resolve, validate, and format the MACA build environment for FlashMLA by adding a new build_tools module and integrating it into setup.py. It also includes comprehensive unit tests for these environment helpers. The review feedback highlights three key improvements: excluding the newly added build_tools package from find_packages in setup.py to prevent namespace pollution, stripping whitespace from environment variables for more robust path resolution, and using idiomatic Path division instead of string formatting when constructing library paths.

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[gemini-code-assist]

Since build_tools has been turned into a Python package by adding build_tools/__init__.py, setuptools.find_packages() will automatically detect and package it. This will result in build_tools being installed as a top-level package in the user's Python environment, polluting the global namespace.

To prevent this, please add "build_tools" to the exclude list of find_packages in setup.py (around line 340).

[gemini-code-assist]

If an environment variable has leading or trailing whitespace (e.g., from copy-pasting), Path might fail to resolve it correctly or is_dir() might return False. Stripping whitespace from the environment variable value before converting it to a Path makes the environment resolution much more robust.

Suggested change

	def _path_from_env(env: Mapping[str, str], name: str) -> Path | None:
	value = env.get(name)
	return Path(value).expanduser() if value else None
	def _path_from_env(env: Mapping[str, str], name: str) -> Path | None:
	value = env.get(name)
	cleaned = value.strip() if value else None
	return Path(cleaned).expanduser() if cleaned else None

[gemini-code-assist]

Using the Path division operator / is more idiomatic and robust in Python than string formatting when constructing paths from Path objects.

Suggested change

	lib_dir = maca_build_env.maca_lib_path
	libraries=["mcblas"]
	extra_objects = ['{}/lib{}.so'.format(lib_dir, l) for l in libraries]
	lib_dir = maca_build_env.maca_lib_path
	libraries = ["mcblas"]
	extra_objects = [str(lib_dir / f"lib{l}.so") for l in libraries]