ImportC + metaprogramming?

[Walter Bright]

In this PR,

https://github.com/dlang/druntime/pull/3670

I added the ability for an ImportC file to import a D file. The initial purpose 
was so that core.stdc.stdarg could be imported to support variadics in C, 
without reimplementing them.

I realized that this actually works - ImportC code can call D code! even use D 
templates!

So then I got to thinking "what the hell have I unleashed?"

I think I just destroyed dtoh.