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/calls/readlinkat_test.c

@@ -31,6 +31,18 @@
 
 char testlib_enable_tmp_setup_teardown;
 
+TEST(readlink, enoent) {
+  char buf[32];
+  ASSERT_SYS(ENOENT, -1, readlink("doesnotexist", buf, 32));
+  ASSERT_SYS(ENOENT, -1, readlink("o/doesnotexist", buf, 32));
+}
+
+TEST(readlink, enotdir) {
+  char buf[32];
+  ASSERT_SYS(0, 0, touch("o", 0644));
+  ASSERT_SYS(ENOTDIR, -1, readlink("o/doesnotexist", buf, 32));
+}
+
 TEST(readlinkat, test) {
   char buf[128], *p, *q;
   memset(buf, -1, sizeof(buf));