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/stack.h

@@ -62,7 +62,7 @@ extern char ape_stack_align[] __attribute__((__weak__));
  * Returns address of bottom of stack.
  */
 #define GetStackAddr(ADDEND) \
-  (((intptr_t)__builtin_frame_address(0) & -GetStackSize()) + (ADDEND))
+  ((((intptr_t)__builtin_frame_address(0) - 1) & -GetStackSize()) + (ADDEND))
 
 /**
  * Returns preferred bottom address of stack.