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

examples/ucontext-sigfpe-recovery.c

@@ -16,12 +16,22 @@
 #include "libc/sysv/consts/sig.h"
 #include "third_party/xed/x86.h"
 
+/**
+ * @fileoverview How to change CPU state on signal delivery
+ *
+ * This program redefines division by zero so that it has a definition.
+ * The definition is the meaning of life, the universe, and everything.
+ * Normally crash signals like `SIGSEGV`, `SIGILL`, and `SIGFPE` aren't
+ * recoverable. This example shows how it actually can be done with Xed
+ * and this example should work on all supported platforms even Windows
+ */
+
 void handler(int sig, siginfo_t *si, ucontext_t *ctx) {
   struct XedDecodedInst xedd;
   xed_decoded_inst_zero_set_mode(&xedd, XED_MACHINE_MODE_LONG_64);
   xed_instruction_length_decode(&xedd, (void *)ctx->uc_mcontext.rip, 15);
   ctx->uc_mcontext.rip += xedd.length;
-  ctx->uc_mcontext.rax = 42;
+  ctx->uc_mcontext.rax = 42;  // set the DIV result registers rdx:rax
   ctx->uc_mcontext.rdx = 0;
 }