Added a stripModifiers() function to remove shared|const|immutable storage classes in D2 (should eventually be moved to a dhelpers file rather than llvm helpers). Replaced a few occurances of STCinvariant with STCimmutable.

module mini.norun_debug3;

void main()
{
    int i = 42;
    int* ip = &i;

    int* fail = cast(int*) 1;
    *fail = 0;
}