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>

extension/third_party/cpython-2.7.18/Lib/compiler/__init__.py

@@ -0,0 +1,31 @@
+"""Package for parsing and compiling Python source code
+
+There are several functions defined at the top level that are imported
+from modules contained in the package.
+
+parse(buf, mode="exec") -> AST
+    Converts a string containing Python source code to an abstract
+    syntax tree (AST).  The AST is defined in compiler.ast.
+
+parseFile(path) -> AST
+    The same as parse(open(path))
+
+walk(ast, visitor, verbose=None)
+    Does a pre-order walk over the ast using the visitor instance.
+    See compiler.visitor for details.
+
+compile(source, filename, mode, flags=None, dont_inherit=None)
+    Returns a code object.  A replacement for the builtin compile() function.
+
+compileFile(filename)
+    Generates a .pyc file by compiling filename.
+"""
+
+import warnings
+
+warnings.warn("The compiler package is deprecated and removed in Python 3.x.",
+              DeprecationWarning, stacklevel=2)
+
+from compiler.transformer import parse, parseFile
+from compiler.visitor import walk
+from compiler.pycodegen import compile, compileFile