Fix bugs and make improvements

- Get clone() working on FreeBSD
- Increase some Python build quotas
- Add more atomic builtins to chibicc
- Fix ASAN poisoning of alloca() memory
- Make MODE= mandatory link path tinier
- Improve the examples folder a little bit
- Start working on some more resource limits
- Make the linenoise auto-complete UI as good as GNU readline
- Update compile.com, avoiding AVX codegen on non-AVX systems
- Make sure empty path to syscalls like opendir raises ENOENT
- Correctly polyfill ENOENT vs. ENOTDIR on the New Technology
- Port bestline's paredit features to //third_party/linenoise
- Remove workarounds for RHEL 5.0 bugs that were fixed in 5.1

libc/str/kstrsignal.S

@@ -64,6 +64,7 @@ kStrSignal:
 	.e	SIGRTMAX,"RTMAX"
 	.e	SIGRTMIN,"RTMIN"
 	.e	SIGEMT,"EMT"
+	.e	SIGPWR,"PWR"
 	.long	0
 	.endobj	kStrSignal,globl,hidden
 	.overrun

libc/str/zipfindcentraldir.c

@@ -1,47 +0,0 @@
-/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
-│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/zip.h"
-
-/* TODO(jart): DELETE */
-
-/**
- * Locates End Of Central Directory record in ZIP file.
- *
- * We search backwards for the End Of Central Directory Record magnum.
- * The ZIP spec says this can be anywhere in the last 64kb. We go all
- * the way since .com.dbg binaries will have lots of DWARF stuff after
- * the embedded .com binary. As such, we sanity check the other fields
- * too to make sure the record seems legit and it's not just a random
- * occurrence of the magnum.
- *
- * @param p points to file memory
- * @param n is byte size of file
- */
-uint8_t *zipfindcentraldir(const uint8_t *p, size_t n) {
-  size_t i;
-  if (n >= kZipCdirHdrMinSize) {
-    i = n - kZipCdirHdrMinSize;
-    do {
-      if (ZIP_CDIR_MAGIC(p + i) == kZipCdirHdrMagic && IsZipCdir32(p, n, i)) {
-        return (/*unconst*/ uint8_t *)(p + i);
-      }
-    } while (i--);
-  }
-  return NULL;
-}