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/hotshot/stones.py

@@ -0,0 +1,30 @@
+import errno
+import hotshot
+import hotshot.stats
+import sys
+import test.pystone
+
+def main(logfile):
+    p = hotshot.Profile(logfile)
+    benchtime, stones = p.runcall(test.pystone.pystones)
+    p.close()
+
+    print "Pystone(%s) time for %d passes = %g" % \
+          (test.pystone.__version__, test.pystone.LOOPS, benchtime)
+    print "This machine benchmarks at %g pystones/second" % stones
+
+    stats = hotshot.stats.load(logfile)
+    stats.strip_dirs()
+    stats.sort_stats('time', 'calls')
+    try:
+        stats.print_stats(20)
+    except IOError, e:
+        if e.errno != errno.EPIPE:
+            raise
+
+if __name__ == '__main__':
+    if sys.argv[1:]:
+        main(sys.argv[1])
+    else:
+        import tempfile
+        main(tempfile.NamedTemporaryFile().name)