[Issue 17868] add pragma(crt_con/destructor)

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17868

--- Comment #7 from Martin Nowak <code at dawg.eu> ---
Let's drop the priority for now, too much hassle to debug OMF and optlink,
wasn't supportable on OSX anyhow.

--