buffer: Fix regression introduced by 6c7eaa and c306a6
Buffer (un)packing was broken on compilers that are not
gcc-compatible since the checks for an argument count of
-1 have been removed from ssh_buffer_(un)pack(). This
fix no longer uses GCC extensions for the VA_NARG
macro, but only plain C99.
Note: The macro can no longer count empty argument lists
(results in compile error) which was not needed anyway.
Signed-off-by: Tilo Eckert <firstname.lastname@example.org>
Reviewed-by: Andreas Schneider <email@example.com>
Reviewed-by: Jakub Jelen <firstname.lastname@example.org>