Remove the notion of "sys*"

- This idea originates from very early in the project and was, at the
  time, a very easy way to categorise things.
- Now, it doesn't really make much sense - it is fairly arbitary, often
  occuring when there is a change in kernel, but not from builder-hex0
  to fiwix, and sysb is in reality completely unnecessary.
- In short, the sys* stuff is a bit of a mess that makes the project
  more difficult to understand.
- This puts everything down into one folder and has a manifest file that
  is used to generate the build scripts on the fly rather than using
  coded scripts.
- This is created in the "seed" stage.

stage0-posix -- (calls) --> seed -- (generates) --> main steps

Alongside this change there are a variety of other smaller fixups to the
general structure of the live-bootstrap rootfs.

- Creating a rootfs has become much simpler and is defined as code in
  go.sh. The new structure, for an about-to-be booted system, is

/
-- /steps (direct copy of steps/)
-- /distfiles (direct copy of distfiles/)
-- all files from seed/*
-- all files from seed/stage0-posix/*

- There is no longer such a thing as /usr/include/musl, this didn't
  really make any sense, as musl is the final libc used. Rather, to
  separate musl and mes, we have /usr/include/mes, which is much easier
  to work with.
- This also makes mes easier to blow away later.
- A few things that weren't properly in packages have been changed;
  checksum-transcriber, simple-patch, kexec-fiwix have all been given
  fully qualified package names.
- Highly breaking change, scripts now exist in their package directory
  but NOT WITH THE packagename.sh. Rather, they use pass1.sh, pass2.sh,
  etc. This avoids manual definition of passes.
  - Ditto with patches; default directory is patches, but then any patch
    series specific to a pass are named patches-passX.

sysa/musl-1.2.4/patches/avoid_sys_clone.patch

@@ -1,18 +0,0 @@
-# SPDX-FileCopyrightText: 2023 Richard Masters <grick23@gmail.com>
-# SPDX-License-Identifier: MIT
---- src/process/posix_spawn.c	2022-04-07 17:12:40.000000000 +0000
-+++ src/process/posix_spawn.c	2023-04-07 12:01:57.217126467 +0000
-@@ -190,8 +190,11 @@
- 		goto fail;
- 	}
- 
--	pid = __clone(child, stack+sizeof stack,
--		CLONE_VM|CLONE_VFORK|SIGCHLD, &args);
-+	pid = fork();
-+	if (pid == 0) {
-+		_exit(child(&args));
-+	}
-+
- 	close(args.p[1]);
- 	UNLOCK(__abort_lock);
-