Make improvements

- Let OpenMP be usable via cosmocc
- Let libunwind be usable via cosmocc
- Make X86_HAVE(AVXVNNI) work correctly
- Avoid using MAP_GROWSDOWN on qemu-aarch64
- Introduce in6addr_any and in6addr_loopback
- Have thread stacks use MAP_GROWSDOWN by default
- Ask OpenMP to not use filesystem to manage threads
- Make NI_MAXHOST and NI_MAXSERV available w/o _GNU_SOURCE

test/libc/calls/getcwd_test.c

@@ -33,7 +33,7 @@ void SetUpOnce(void) {
 }
 
 TEST(__getcwd, zero) {
-  if (IsQemu()) return;
+  if (IsQemuUser()) return;
   ASSERT_SYS(ERANGE, -1, __getcwd(0, 0));
 }