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/vga.c

@@ -15,6 +15,8 @@
 #include "libc/str/str.h"
 #include "libc/sysv/consts/termios.h"
 
+#ifdef __x86_64__
+
 /**
  * @fileoverview Bare Metal VGA TTY demo.
  *
@@ -58,3 +60,5 @@ int main(int argc, char *argv[]) {
     }
   }
 }
+
+#endif /* __x86_64__ */