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

libc/calls/sigaction.c

@@ -42,6 +42,8 @@
 #include "libc/sysv/consts/sig.h"
 #include "libc/sysv/errfuns.h"
 
+#undef sigaction
+
 #ifdef SYSDEBUG
 STATIC_YOINK("strsignal");  // for kprintf()
 #endif
@@ -75,9 +77,9 @@ union metasigaction {
   struct sigaction_xnu_out xnu_out;
 };
 
-void __sigenter_netbsd(int, void *, void *);
-void __sigenter_freebsd(int, void *, void *);
-void __sigenter_openbsd(int, void *, void *);
+void __sigenter_netbsd(int, void *, void *) hidden;
+void __sigenter_freebsd(int, void *, void *) hidden;
+void __sigenter_openbsd(int, void *, void *) hidden;
 
 static void sigaction_cosmo2native(union metasigaction *sa) {
   if (!sa) return;
@@ -279,7 +281,7 @@ static int __sigaction(int sig, const struct sigaction *act,
  *   `SA_NOMASK` for this flag, which means the same thing.
  *
  * - `SA_NOCLDWAIT`: Changes `SIGCHLD` so the zombie is gone and you
- *   can't call `wait()` anymore; similar to SIGCHLD + SIG_IGN but may
+ *   can't call `wait()` anymore; similar but may
  *   still deliver the SIGCHLD.
  *
  * - `SA_NOCLDSTOP`: Lets you set `SIGCHLD` handler that's only notified
@@ -435,7 +437,7 @@ static int __sigaction(int sig, const struct sigaction *act,
  * @asyncsignalsafe
  * @vforksafe
  */
-int(sigaction)(int sig, const struct sigaction *act, struct sigaction *oldact) {
+int sigaction(int sig, const struct sigaction *act, struct sigaction *oldact) {
   int rc;
   char buf[2][128];
   if (sig == SIGKILL || sig == SIGSTOP) {