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/Modules/future_builtins.c

@@ -0,0 +1,105 @@
+
+/* future_builtins module */
+
+/* This module provides functions that will be builtins in Python 3.0,
+   but that conflict with builtins that already exist in Python
+   2.x. */
+
+
+#include "Python.h"
+
+PyDoc_STRVAR(module_doc,
+"This module provides functions that will be builtins in Python 3.0,\n\
+but that conflict with builtins that already exist in Python 2.x.\n\
+\n\
+Functions:\n\
+\n\
+ascii(arg) -- Returns the canonical string representation of an object.\n\
+filter(pred, iterable) -- Returns an iterator yielding those items of \n\
+       iterable for which pred(item) is true.\n\
+hex(arg) -- Returns the hexadecimal representation of an integer.\n\
+map(func, *iterables) -- Returns an iterator that computes the function \n\
+    using arguments from each of the iterables.\n\
+oct(arg) -- Returns the octal representation of an integer.\n\
+zip(iter1 [,iter2 [...]]) -- Returns a zip object whose .next() method \n\
+    returns a tuple where the i-th element comes from the i-th iterable \n\
+    argument.\n\
+\n\
+The typical usage of this module is to replace existing builtins in a\n\
+module's namespace:\n \n\
+from future_builtins import ascii, filter, map, hex, oct, zip\n");
+
+static PyObject *
+builtin_hex(PyObject *self, PyObject *v)
+{
+    return PyNumber_ToBase(v, 16);
+}
+
+PyDoc_STRVAR(hex_doc,
+"hex(number) -> string\n\
+\n\
+Return the hexadecimal representation of an integer or long integer.");
+
+
+static PyObject *
+builtin_oct(PyObject *self, PyObject *v)
+{
+    return PyNumber_ToBase(v, 8);
+}
+
+PyDoc_STRVAR(oct_doc,
+"oct(number) -> string\n\
+\n\
+Return the octal representation of an integer or long integer.");
+
+
+static PyObject *
+builtin_ascii(PyObject *self, PyObject *v)
+{
+    return PyObject_Repr(v);
+}
+
+PyDoc_STRVAR(ascii_doc,
+"ascii(object) -> string\n\
+\n\
+Return the same as repr().  In Python 3.x, the repr() result will\n\
+contain printable characters unescaped, while the ascii() result\n\
+will have such characters backslash-escaped.");
+
+/* List of functions exported by this module */
+
+static PyMethodDef module_functions[] = {
+    {"hex",             builtin_hex,        METH_O, hex_doc},
+    {"oct",             builtin_oct,        METH_O, oct_doc},
+    {"ascii",           builtin_ascii,      METH_O, ascii_doc},
+    {NULL,              NULL}   /* Sentinel */
+};
+
+
+/* Initialize this module. */
+
+PyMODINIT_FUNC
+initfuture_builtins(void)
+{
+    PyObject *m, *itertools, *iter_func;
+    char *it_funcs[] = {"imap", "ifilter", "izip", NULL};
+    char **cur_func;
+
+    m = Py_InitModule3("future_builtins", module_functions, module_doc);
+    if (m == NULL)
+        return;
+
+    itertools = PyImport_ImportModuleNoBlock("itertools");
+    if (itertools == NULL)
+        return;
+
+    /* If anything in the following loop fails, we fall through. */
+    for (cur_func = it_funcs; *cur_func; ++cur_func){
+        iter_func = PyObject_GetAttrString(itertools, *cur_func);
+        if (iter_func == NULL ||
+            PyModule_AddObject(m, *cur_func+1, iter_func) < 0)
+            break;
+    }
+    Py_DECREF(itertools);
+    /* any other initialization needed */
+}