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/musl/Makefile

@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: Apache-2.0
+# musl libc — MIT-licensed: https://musl.libc.org/
+#
+# Installs into $(PREFIX) (= build/ports/musl/prefix), which port.mk exports
+# to every other port as $(MUSL). Nothing is written into this directory.
+
+include ../mk/port.mk
+
+MUSL_VERSION := 1.2.5
+MUSL_URL     := https://musl.libc.org/releases/musl-$(MUSL_VERSION).tar.gz
+MUSL_SHA256  := a9a118bbe84d8764da0ea0d28b3ab3fae8477fc7e4085d90102b8596fc7c75e4
+
+TARBALL := $(DISTDIR)/musl-$(MUSL_VERSION).tar.gz
+
+$(TARBALL): | $(DISTDIR)
+	curl -fsSL -o $@ $(MUSL_URL)
+	echo "$(MUSL_SHA256)  $@" | sha256sum -c -
+
+download: $(TARBALL)
+
+$(SRCDIR): $(TARBALL)
+	mkdir -p $(PORTDIR)
+	tar -xzf $< -C $(PORTDIR)
+	mv $(PORTDIR)/musl-$(MUSL_VERSION) $@
+
+# $(SRCDIR) is order-only (|) on purpose. The stamp lives INSIDE $(SRCDIR),
+# so creating it bumps that directory's mtime — making the directory forever
+# newer than the stamp it contains, and re-running this rule on every single
+# build. The second run then fails, because the patch does not apply twice.
+$(SRCDIR)/.patched: patches/0001-schunix-tls.patch | $(SRCDIR)
+	cd $(SRCDIR) && patch -p1 < $(CURDIR)/patches/0001-schunix-tls.patch
+	touch $@
+
+$(BUILDDIR)/config.mak: $(SRCDIR)/.patched
+	mkdir -p $(BUILDDIR)
+	cd $(BUILDDIR) && $(SRCDIR)/configure \
+		--prefix=$(PREFIX) \
+		--disable-shared \
+		CC=$(CC) \
+		CFLAGS="-D__SCHUNIX__ -fno-stack-protector"
+
+$(BUILDDIR)/lib/libc.a: $(BUILDDIR)/config.mak
+	$(MAKE) -C $(BUILDDIR)
+
+$(PREFIX)/lib/libc.a: $(BUILDDIR)/lib/libc.a
+	$(MAKE) -C $(BUILDDIR) install
+
+install: $(PREFIX)/lib/libc.a
+
+clean:
+	rm -rf $(PORTDIR)
+
+distclean: clean
+	rm -f $(TARBALL)