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
{
    int i;
    void p()
    {
        printf("%d\n", i);
    }
}

void main()
{
    printf("should print 4\n");
    C c = new C;
    c.i = 4;
    c.p();
    //delete c;
}