* x86-64-tdep.c: Fix some formatting problems, mostly in comments.

* x86-64-tdep.c: Fix some formatting problems, mostly in comments.
(x86_64_push_return_address): Add comment.
(x86_64_pop_frame): Make static.
(examine_argument): Clarify comment.
(x86_64_skip_prologue): Make prolog_expact variable static.