ltrace: implement x86_64 arch specifics.

fix trace build on x86_64

Change-Id: I205bd9eee03efea9e298c2877cc0a6440770caf0
Reviewed-on: https://review.haiku-os.org/c/1148
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>