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/crctable.c

@@ -34,7 +34,7 @@ static textstartup void BZ2_crc32Table_init() {
     BZ2_crc32Table[i] = u;
   }
   if (BZ2_crc32Table[0] || BZ2_crc32Table[255] != 0xb1f740b4) {
-    asm("hlt");
+    __builtin_trap();
   }
 }