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 tangotests.sync3;

void main()
{
    int i = foo();
}

int foo()
{
    int res;
    synchronized
    {
        scope(exit) res--;
        res++;
        return res;
    }
}