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/symlinkat.c

@@ -34,7 +34,7 @@
  * @param target can be relative and needn't exist
  * @param linkpath is what gets created
  * @return 0 on success, or -1 w/ errno
- * @note Windows NT only lets admins do this
+ * @raise EPERM if a non-admin on Windows NT tries to use this
  * @asyncsignalsafe
  */
 int symlinkat(const char *target, int newdirfd, const char *linkpath) {