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/calls/pipe.c

@@ -28,12 +28,16 @@
  *
  * @param fd is (reader, writer)
  * @return 0 on success or -1 w/ errno
+ * @raise EFAULT if pipefd is NULL or an invalid address
+ * @raise EMFILE if RLIMIT_NOFILE is exceedde
  * @asyncsignalsafe
  * @see pipe2()
  */
 int pipe(int pipefd[hasatleast 2]) {
   int rc;
-  if (IsAsan() && !__asan_is_valid(pipefd, sizeof(int) * 2)) {
+  if (!pipefd || (IsAsan() && !__asan_is_valid(pipefd, sizeof(int) * 2))) {
+    // needed for windows which is polyfilled
+    // needed for xnu and netbsd which don't take an argument
     rc = efault();
   } else if (!IsWindows()) {
     rc = sys_pipe(pipefd);