port 2P step 1: vendor CPython 2.7.18 as the mtpython static library

The embedded 40250 script layer needs its own interpreter on five platforms.
2.7 is end-of-life, so nothing can be fetched from the target SDKs and the
source is vendored (official 2.7.18 tarball, trimmed to 25MB; Lib/ stays for
step 3's python27.zip).

cpython-2.7.18/CMakeLists.txt builds one `mtpython` static library from exactly
the 133 objects the reference libpython2.7.a contains, off by default behind
-DMTGODOT_EMBED_PYTHON=ON. The source list and the built-in module table
(config/config.c, 39 entries) are shared; pyconfig.h is a probe result and is
not, so each platform keeps its own under config/<platform>/, regenerated by
tools/py_embed/gen_pyconfig.sh and checked against the shared table.

Three vendor patches, documented in docs/THIRD-PARTY.md: configure/configure.ac
learn arm64 on macOS, and posixmodule.c undefines the process-control calls it
hard-defines past pyconfig.h when building for iOS.

macOS (ctest python.embed: every builtin imports, codecs and pickle work off the
vendored Lib/), Android arm64 and iOS arm64 build. Linux needs a Linux host and
Windows needs a MinGW-vs-MSVC decision; both are noted for step 4.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/PYTHON-EMBED-EVAL.md

@@ -96,8 +96,11 @@ Godot 这边只剩一个宿主 Control：把输入转发给 `CPythonWindowManage
 
 ## 下一步
 
-1. 把 CPython 2.7.18 放进 `extension/third_party/`，共用源码/静态模块清单，但为 macOS、Linux、Windows、
-   Android、iOS 分别生成或维护 `pyconfig.h`，静态链接进 `libmtgodot`；
+1. ~~把 CPython 2.7.18 放进 `extension/third_party/`，共用源码/静态模块清单，但为 macOS、Linux、Windows、
+   Android、iOS 分别生成或维护 `pyconfig.h`~~，静态链接进 `libmtgodot`；
+   源码和三平台配置已完成（2026-09-23，批次 2P step 1）：`mtpython` 静态库（`-DMTGODOT_EMBED_PYTHON=ON`）、
+   `tools/py_embed/gen_pyconfig.sh`、ctest `python.embed`；macOS/Android/iOS 编译通过，Linux 缺主机、
+   Windows 的 MinGW 冲突见 `docs/THIRD-PARTY.md`。静态链接进 `libmtgodot` 是 step 2；
 2. `pack` 模块走 `asset_io`，继续负责 40250 的 root/uiscript。标准库沿用已验证的 `python27.zip + sys.path`
    方案：桌面端放在解释器可读的真实文件系统路径，移动端首次启动从应用资源复制到应用沙盒并校验 sha256；静态启用
    `zipimport`。不要依赖 `system.py` 的简单 `name + '.py'` 钩子加载带 package/dotted import 的标准库；