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

third_party/chibicc/chibicc.h

@@ -348,6 +348,8 @@ typedef enum {
   ND_LOAD,        // Atomic load
   ND_TESTANDSET,  // Atomic lock test and set
   ND_RELEASE,     // Atomic lock release
+  ND_FETCHADD,    // Atomic fetch and add
+  ND_SUBFETCH,    // Atomic sub and fetch
   ND_FPCLASSIFY,  // floating point classify
   ND_MOVNTDQ,     // Intel MOVNTDQ
   ND_PMOVMSKB,    // Intel PMOVMSKB