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

tool/hello/hello.c

@@ -9,11 +9,6 @@ static ssize_t Write(int fd, const char *s) {
 }
 
 int main(int argc, char *argv[]) {
-  wchar_t B1[8];
-  wchar_t B2[8];
-  B1[1] = L'\0';
-  B2[1] = L'\0';
   Write(1, "hello world\n");
-  kprintf("%x\n", wcscmp(memcpy(B1, "\xff\xff\xff\x7f", 4),
-                         memcpy(B2, "\x00\x00\x00\x80", 4)));
+  kprintf("hello world\n");
 }