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/setrlimit.c

@@ -44,11 +44,20 @@
  *   when the hard limit is exceeded. It works everywhere but Windows
  *
  * - `RLIMIT_NPROC` limits the number of simultaneous processes and it
- *   should work on all platforms except Windows.
+ *   should work on all platforms except Windows. Please be advised it
+ *   limits the process, with respect to the activities of the user id
+ *   as a whole.
  *
  * - `RLIMIT_NOFILE` limits the number of open file descriptors and it
  *   should work on all platforms except Windows (TODO)
  *
+ * The rlimit magnums differ for each platform but occupy the interval
+ * zero through `RLIM_NLIMITS`. Usually they're set to `RLIM_INFINITY`
+ * which is `-1` on Linux/Windows, and `LONG_MAX` on BSDs. In any case
+ * they're both very large numbers under the Cosmopolitan unsigned ABI
+ * because struct rlimit uses uint64_t. The special magnum 127 is used
+ * for constant values that aren't supported by the host platform.
+ *
  * @param rlim specifies new resource limit
  * @return 0 on success or -1 w/ errno
  * @see libc/sysv/consts.sh