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/sysv/calls/__sys_sigprocmask.s

@@ -0,0 +1,2 @@
+.include "o/libc/sysv/macros.internal.inc"
+.scall __sys_sigprocmask,0x125030154214900e,globl,hidden

libc/sysv/calls/clone.s

@@ -1,2 +0,0 @@
-.include "o/libc/sysv/macros.internal.inc"
-.scall clone,0xfffffffffffff038,globl

libc/sysv/calls/sys_clone.s

@@ -0,0 +1,2 @@
+.include "o/libc/sysv/macros.internal.inc"
+.scall sys_clone,0x11fffffffffff038,globl,hidden

libc/sysv/calls/sys_sigprocmask.s

@@ -1,2 +0,0 @@
-.include "o/libc/sysv/macros.internal.inc"
-.scall sys_sigprocmask,0x125030154214900e,globl,hidden