@nogc required on C API callbacks?

[Brian Schott via Digitalmars-d]

https://github.com/D-Programming-Language/druntime/blob/master/src/core/stdc/signal.d

When @nogc was added to the top of that file, the type of sigfn_t 
changed from "void function(int) extern (C) @system nothrow" to 
"void function(int) extern (C) @system nothrow @nogc".

This breaks some code such as the ae library used by Digger. (The 
@nogc annotation is now required on signal handlers). The 
argument for requiring @nogc on C library callbacks makes sense 
to me, so I'd like to know if this was intentional.