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/calls.mk

@@ -110,6 +110,7 @@ o/$(MODE)/libc/calls/execle.o				\
 o/$(MODE)/libc/calls/execlp.o				\
 o/$(MODE)/libc/calls/execve-nt.o			\
 o/$(MODE)/libc/calls/execve-sysv.o			\
+o/$(MODE)/libc/calls/readlinkat-nt.o			\
 o/$(MODE)/libc/calls/mkntenvblock.o:			\
 		OVERRIDE_CPPFLAGS +=			\
 			-DSTACK_FRAME_UNLIMITED