Make cli commands yoinkable into cosmo shell

This lets our system() and popen() commands function sort of like
BusyBox and ToyBox. By default the Cosmopolitan Shell is lightweight.
But if you use STATIC_YOINK then you can pull the individual commands
you want into the linkage, and they'll be included in a single binary.
For example the demo binary embeds `tr` and `sed` and ends up ~140kb.

third_party/sed/main.c

@@ -1,6 +1,4 @@
-// clang-format off
 /*	$NetBSD: main.c,v 1.36 2020/05/15 22:39:54 christos Exp $	*/
-
 /*-
  * Copyright (c) 2013 Johann 'Myrkraverk' Oskarsson.
  * Copyright (c) 1992 Diomidis Spinellis.
@@ -34,85 +32,20 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
-
-#include "libc/calls/makedev.h"
-#include "libc/calls/weirdtypes.h"
-#include "libc/intrin/newbie.h"
-#include "libc/calls/typedef/u.h"
-#include "libc/calls/weirdtypes.h"
-#include "libc/sock/select.h"
-#include "libc/sysv/consts/endian.h"
-#include "libc/calls/calls.h"
-#include "libc/calls/weirdtypes.h"
-#include "libc/runtime/runtime.h"
-#include "libc/sysv/consts/map.h"
-#include "libc/sysv/consts/mlock.h"
-#include "libc/sysv/consts/msync.h"
-#include "libc/sysv/consts/posix.h"
-#include "libc/sysv/consts/prot.h"
-#include "libc/sysv/consts/madv.h"
-#include "libc/sysv/consts/mfd.h"
-#include "libc/sysv/consts/mremap.h"
-#include "libc/intrin/newbie.h"
-#include "libc/calls/calls.h"
-#include "libc/calls/struct/rlimit.h"
-#include "libc/calls/struct/rusage.h"
-#include "libc/calls/sysparam.h"
-#include "libc/calls/weirdtypes.h"
-#include "libc/limits.h"
-#include "libc/sysv/consts/endian.h"
-#include "libc/sysv/consts/prio.h"
-#include "libc/sysv/consts/rlim.h"
-#include "libc/sysv/consts/rlimit.h"
-#include "libc/sysv/consts/rusage.h"
 #include "libc/calls/calls.h"
 #include "libc/calls/struct/stat.h"
-#include "libc/calls/struct/stat.macros.h"
-#include "libc/calls/weirdtypes.h"
-#include "libc/sysv/consts/s.h"
-#include "libc/sysv/consts/utime.h"
-#include "libc/calls/calls.h"
-#include "libc/runtime/runtime.h"
-#include "libc/time/time.h"
-
-#include "libc/log/bsd.h"
-#include "libc/errno.h"
-#include "libc/calls/calls.h"
-#include "libc/sysv/consts/at.h"
-#include "libc/sysv/consts/f.h"
-#include "libc/sysv/consts/fd.h"
-#include "libc/sysv/consts/o.h"
-// MISSING #include <libgen.h>
-#include "libc/limits.h"
-#include "libc/sysv/consts/_posix.h"
-#include "libc/str/locale.h"
-#include "third_party/regex/regex.h"
-
-#define _WITH_GETLINE
-#include "libc/calls/calls.h"
 #include "libc/fmt/fmt.h"
-#include "libc/stdio/lock.internal.h"
-#include "libc/stdio/stdio.h"
-#include "libc/stdio/temp.h"
-#include "libc/mem/alg.h"
-#include "libc/fmt/conv.h"
-#include "libc/mem/mem.h"
-#include "libc/stdio/rand.h"
+#include "libc/log/bsd.h"
 #include "libc/runtime/runtime.h"
-#include "libc/stdio/temp.h"
-#include "libc/sysv/consts/exit.h"
-#include "third_party/gdtoa/gdtoa.h"
-#include "libc/mem/alg.h"
+#include "libc/stdio/stdio.h"
+#include "libc/str/locale.h"
 #include "libc/str/str.h"
-#include "libc/calls/calls.h"
-#include "libc/calls/weirdtypes.h"
-#include "libc/sysv/consts/fileno.h"
-#include "libc/sysv/consts/o.h"
-#include "libc/sysv/consts/ok.h"
+#include "libc/sysv/consts/s.h"
 #include "third_party/getopt/getopt.h"
-
+#include "third_party/sed/cmd.h"
 #include "third_party/sed/defs.h"
 #include "third_party/sed/extern.h"
+// clang-format off
 
 /*
  * Linked list of units (strings and files) to be compiled
@@ -169,7 +102,7 @@ static void add_file(char *);
 static void usage(void) wontreturn;
 
 int
-main(int argc, char *argv[])
+_sed(int argc, char *argv[])
 {
 	int c, fflag;
 	char *temp_arg;
@@ -260,7 +193,7 @@ main(int argc, char *argv[])
 static void
 usage(void)
 {
-	(void)fprintf(stderr,
+	(void)(fprintf)(stderr,
 	    "Usage:  %s [-aElnru] command [file ...]\n"
 	    "\t%s [-aElnru] [-e command] [-f command_file] [-I[extension]]\n"
 	    "\t    [-i[extension]] [file ...]\n", program_invocation_name,