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.

extern(C) int printf(char*, ...);

class C
{
    void dump()
    {
        printf("C dumped\n");
    }
}

void heap()
{
    auto c = new C;
    c.dump();
}

void stack()
{
    scope c = new C;
    c.dump();
}

void main()
{
    heap();
    stack();
}