Fix handling of Quad-type arguments. Previously, syscalls
containing 64-bit arguments would have explicit padding.
On 64-bit platforms there was no padding, so the dummy
argument was not covering anything. On 32-bit platforms
with weak alignment (i.e. i386) the 64-bit argument did
not need to be aligned, so there too an aditional argument
was introduced. On 32-bit platforms with strong alignment
(i.e. PowerPC) the dummy argument in fact cover the padding.
By elimininating the dummy argument, 64-bit platforms now
have 1 argument less. This also applies to 32-bit platforms
with weak alignment. On PowerPC this doesn't matter, because
the padding is still there. We just don't "name" it.
Deal with those 3 cases.

Approved by: re (kensmith)