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

examples/breakpoint.c

@@ -23,13 +23,7 @@ int main(int argc, char *argv[]) {
     kprintf("try running: o//tool/build/strace.com %s%n", argv[0]);
   }
 
-  asm volatile("mov\t%4,%%r10\n\t"
-               "mov\t%5,%%r8\n\t"
-               "mov\t%6,%%r9\n\t"
-               "int3"
-               : /* no outputs */
-               : "a"(0), "D"(1), "S"(2), "d"(3), "g"(4), "g"(5), "g"(6)
-               : "r8", "r9", "r10");
+  __builtin_trap();
 
   printf("recovered from SIGTRAP without handler\r\n");
   return 0;