Fix the problems exposed by the callingconv1.d test case. The first was that unless otherwise specified, inputs are assumed to be in registers even if they specify a "matching output" that's in memory. While testing that fix, I also ran into a bug causing the generated "matching output" for any input was always the first one instead of the correct one.

module tangotests.volatile1;

import tango.stdc.stdlib;

void main()
{
    int var = rand();
    {
        int i = var;
        volatile;
        int j = i;
    }
}