Fixed DStress tests nocompile/c/{const_32_B.d,const_32_C.d}. Updated the runtest script to build libtangobos-partial.a if it hasn't already been built. Added in signbit() and va_arg!()() to libtangobos-partial.a so more of the phobos dependent DStress tests pass.

module bug47;

bool func(bool a, bool b)
{
    if (a) b = false;
    return b;
}

void main()
{
    assert(func(0,0) == 0);
    assert(func(0,1) == 1);
    assert(func(1,0) == 0);
    assert(func(1,1) == 0);
}