DRuntime Change for DMD#3727

[Orvid]

Added a method for the DMD fix to an issue with delete that was uncovered while working on #864

These are the changes required in order for dlang/dmd#3727 to be able to pass the tests.

[rainers]

I always wonder what these empty comments are meant to accomplish. Please add something like "called for 'delete p' if p points to a struct with a destructor, but without operator delete being overloaded."

[rainers]

Let's move on with this. We should add a unittest here, but it won't work before this PR and the one in DMD are both merged.

[rainers]

Auto-merge toggled on

[rainers]

Here is a possible test, though it triggered some more bugs...

import core.memory;

struct S
{
    ~this() {}
    ubyte data[32];
}

version = dmd2065; // need a second block to circumvent bug in caching before dmd 2.066

void main()
{
    S* s = new S;
    version(dmd2065) S* t = new S; 
    S* p = s;
    auto inf = GC.query(p);
    assert(inf.attr & GC.BlkAttr.NO_SCAN);
    delete s;
    version(dmd2065) inf = GC.query(t); // invalidate cache info
    inf = GC.query(p); // crashes if S.sizeof > 2048
    assert(!(inf.attr & GC.BlkAttr.NO_SCAN));
}