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/mksh/Makefile

@@ -0,0 +1,45 @@
+# SPDX-License-Identifier: Apache-2.0
+# mksh (MirBSD Korn Shell) — permissive: https://www.mirbsd.org/mksh.htm
+# Installed as /bin/sh — Schunix standardizes on "sh" as the one shell name;
+# no ksh/dash/other aliases are installed or looked up by init.
+
+include ../mk/port.mk
+
+MKSH_VERSION := R59c
+MKSH_URL     := http://www.mirbsd.org/MirOS/dist/mir/mksh/mksh-$(MKSH_VERSION).tgz
+
+TARBALL := $(DISTDIR)/mksh-$(MKSH_VERSION).tgz
+
+CFLAGS  := -static -D__SCHUNIX__ -I$(MUSL)/include -fno-stack-protector
+LDFLAGS := -static -L$(MUSL)/lib -lc
+
+$(TARBALL): | $(DISTDIR)
+	curl -fsSL --tlsv1.0 -o $@ $(MKSH_URL)
+
+download: $(TARBALL)
+
+$(SRCDIR): $(TARBALL)
+	mkdir -p $(PORTDIR)
+	tar -xzf $< -C $(PORTDIR)
+	mv $(PORTDIR)/mksh $@
+
+# Order-only (|) on $(SRCDIR): the extracted tarball never changes, so a
+# directory mtime should not trigger a rebuild of an already-built shell.
+$(BUILDDIR)/lksh: | $(SRCDIR)
+	mkdir -p $(BUILDDIR)
+	cd $(BUILDDIR) && \
+		CC="$(CC)" CFLAGS="$(CFLAGS)" LDFLAGS="$(LDFLAGS)" \
+		sh $(SRCDIR)/Build.sh -r -L
+
+$(SYSROOT)/bin/sh: $(BUILDDIR)/lksh | $(SYSROOT)/bin
+	cp $< $@
+	chmod 755 $@
+
+install: $(SYSROOT)/bin/sh
+
+
+clean:
+	rm -rf $(PORTDIR)
+
+distclean: clean
+	rm -f $(TARBALL)