Make considerably more progress on AARCH64

- Utilities like pledge.com now build
- kprintf() will no longer balk at 48-bit addresses
- There's a new aarch64-dbg build mode that should work
- gc() and defer() are mostly pacified; avoid using them on aarch64
- THIRD_PART_STB now has Arm Neon intrinsics for fast image handling

libc/sysv/errno.c

@@ -18,11 +18,6 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/errno.h"
 
-asm(".weak\t__asan_init");
-asm(".weak\t__asan_register_globals");
-asm(".weak\t__asan_unregister_globals");
-asm(".weak\t__asan_version_mismatch_check_v8");
-
 /**
  * Global variable for last error.
  *