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/runtime/printargs.greg.c

@@ -240,9 +240,9 @@ textstartup void __printargs(const char *prologue) {
   PRINT("FILE DESCRIPTORS");
   for (i = 0; i < ARRAYLEN(pfds); ++i) {
     pfds[i].fd = i;
-    pfds[i].events = POLLIN | POLLOUT;
+    pfds[i].events = POLLIN;
   }
-  if ((n = poll(pfds, ARRAYLEN(pfds), 20)) != -1) {
+  if ((n = poll(pfds, ARRAYLEN(pfds), 0)) != -1) {
     for (i = 0; i < ARRAYLEN(pfds); ++i) {
       if (i && (pfds[i].revents & POLLNVAL)) continue;
       PRINT(" ☼ %d (revents=%#hx F_GETFL=%#x)", i, pfds[i].revents,