Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

ports/Makefile

@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: Apache-2.0
+# Schunix ports — third-party software, one directory per port.
+# All ports are permissive-licensed (MIT, BSD, 0BSD, Apache 2.0).
+#
+#   ports/musl/    libc — installs headers/libs to build/ports/musl/prefix
+#   ports/mksh/    MirBSD Korn Shell — installed as sysroot/bin/sh
+#   ports/toybox/  core utilities — installed as sysroot/bin/<applet>
+#
+# A port directory holds only a Makefile and optional patches/. Everything
+# generated lives in build/ports/<name>/ — see mk/port.mk for the contract.
+# Tarballs are cached in dist/ and are never removed by 'clean'.
+#
+# Order matters: musl must be built before anything that links against it.
+
+# Ports that live in this directory but are deliberately not built by `make`.
+# Empty for now; the filter stays because the reason it existed will recur --
+# a port whose licence cannot be combined with Apache-2.0 can be kept here for
+# local testing but must never be built into a Schunix image.
+NOTPORTS :=
+PORTS := $(filter-out $(NOTPORTS), \
+           $(patsubst %/,%,$(sort $(dir $(wildcard */Makefile)))))
+
+.PHONY: all $(PORTS) clean distclean
+
+all: $(PORTS)
+
+mksh:   musl
+toybox: musl
+
+$(PORTS):
+	$(MAKE) -C $@
+
+clean distclean:
+	for p in $(PORTS); do $(MAKE) -C $$p $@; done