On D's garbage collection

[Marcel]

I'm been thinking about using D in conjunction with C11 to 
develop a set of applications with hard real-time requirements. 
While initially the goal was to use C++ instead, it has become 
clear that D's introspection facilities will offer significant 
advantages. Unfortunately, the project will heavily rely on 
custom memory allocators written in C, so the presence of garbage 
collection in the language is a problem. While I'm aware that the 
nogc attribute exists, I haven't actually seen a way to apply it 
to a whole project. Is this possible?