Align a variable on the stack.

[Marc Schütz via Digitalmars-d-learn]

Ok, benchA and benchB have the same assembler code generated. 
However, I _can_ reproduce the slowdown albeit on average only 
20%-40%, not a factor of 10.

It turns out that it's always the first tested function that's 
slower. You can test this by switching benchA and benchB in the 
call to benchmark(). I suspect the reason is that the OS is 
paging in the code the first time, and we're actually seeing the 
cost of the page fault. If you a second round of benchmarks after 
the first one, that one shows more or less the same performance 
for both functions.