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/ld_so_beos

@@ -0,0 +1,78 @@
+#! /bin/sh
+#
+# linkmodule for Python
+# Chris Herborth (chrish@qnx.com)
+#
+# This is covered by the same copyright/licensing terms as the rest of
+# Python.
+#
+# Shell script to build shared library versions of the modules; since
+# the change to the *ahem* "proper" import/export mechanism, this script
+# is much simpler.  It handles PowerPC and x86, too.
+#
+# This is called by the Modules/Makefile as $(LDSHARED):
+#
+# $(LDSHARED) foomodule.o -o foomodule$(SO)
+#
+# Could also be called as:
+#
+# $(LDSHARED)  readline.o  -L/boot/home/config/lib -lreadline -ltermcap \
+# -o readline$(SO)
+#
+# so we need to preserve the arguments, sort of.
+
+# Make sure we got reasonable arguments.
+TARGET=""
+ARGS=""
+
+while [ "$#" != "0" ]; do
+	case "$1" in
+		-o)	TARGET="$2"; shift; shift;;
+		*)	ARGS="$ARGS $1"; shift;;
+	esac
+done
+
+if [ "$TARGET" = "" ] ; then
+	echo "Usage:"
+	echo
+	echo "	$0 [args] -o foomodule.so [args] foomodule.o [args]"
+	echo
+	echo "Where:"
+	echo
+	echo "	[args]	normal compiler arguments"
+	exit 1
+fi
+
+# The shared libraries and glue objects we need to link against; these
+# libs are overkill for most of the standard modules, but it makes life
+# in this shell script easier.
+LIBS="-lbe -lnet -lroot"
+
+case $BE_HOST_CPU in
+	ppc)
+		# Boy, do we need a lot of crap...
+		GLUE_LOC=/boot/develop/lib/ppc
+		GLUE="${GLUE_LOC}/glue-noinit.a ${GLUE_LOC}/init_term_dyn.o"
+		case $(uname -r) in
+			4.0*) CC="mwcc -xms -export pragma -nodup" ;;
+			*) CC="mwcc -shared -export pragma -nodup" ;;
+		esac
+		;;
+
+	x86)
+		# We don't need as much crap here...
+		GLUE=""
+		CC="gcc -nostart -Wl,-soname=${TARGET}"
+		;;
+
+	*)
+		# What the?!?
+		echo "$0 doesn't support $BE_HOST_CPU systems..."
+		echo "You're on your own... I'd be surprised if this works."
+		GLUE=""
+		CC="cc"
+		;;
+esac
+
+# Now link that shared lib...
+$CC -o $TARGET $ARGS $GLUE $LIBS