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 bug15;

bool bool1(bool b) {
    if (b) return true;
    else return false;
}

bool bool2(bool b) {
    if (b) {return true;}
    else {return false;}
}

void main()
{
    assert(bool1(true));
    assert(!bool2(false));
}