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

libc/nexgen32e/program_invocation_name2.c

@@ -18,4 +18,8 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/runtime/runtime.h"
 
+#ifndef __x86_64__
+
 char *program_invocation_name;
+
+#endif /* __x86_64__ */