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

third_party/bzip2/bz_internal_error.c

@@ -18,5 +18,5 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 
 void bz_internal_error(int err) {
-  asm("hlt");
+  __builtin_trap();
 }