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-nt.c

@@ -31,7 +31,6 @@ textwindows int sys_pipe_nt(int pipefd[2], unsigned flags) {
   int64_t hin, hout;
   int reader, writer;
   char16_t pipename[64];
-  if (!pipefd) return efault();
   CreatePipeName(pipename);
   if ((reader = __reservefd(-1)) == -1) return -1;
   if ((writer = __reservefd(-1)) == -1) {