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

test/libc/runtime/mmap_test.c

@@ -196,6 +196,7 @@ TEST(mmap, cowFileMapReadonlyFork) {
   }
   EXPECT_STREQN("hello", p, 5);
   EXPECT_NE(-1, munmap(p, 6));
+  EXPECT_NE(-1, close(fd));
   EXPECT_NE(-1, unlink(path));
 }