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

tool/build/compile.c

@@ -40,6 +40,7 @@
 #include "libc/math.h"
 #include "libc/mem/mem.h"
 #include "libc/nexgen32e/kcpuids.h"
+#include "libc/nexgen32e/x86feature.h"
 #include "libc/runtime/runtime.h"
 #include "libc/runtime/sysconf.h"
 #include "libc/stdio/append.internal.h"
@@ -841,6 +842,12 @@ int main(int argc, char *argv[]) {
     if (isclang && IsGccOnlyFlag(argv[i])) {
       continue;
     }
+    if (!X86_HAVE(AVX) &&
+        (!strcmp(argv[i], "-msse2avx") || !strcmp(argv[i], "-Wa,-msse2avx"))) {
+      // Avoid any chance of people using Intel's older or low power
+      // CPUs encountering a SIGILL error due to these awesome flags
+      continue;
+    }
     if (!strcmp(argv[i], "-w")) {
       AddArg(argv[i]);
       AddArg("-D__W__");