[D-runtime] Should import file generation depend on MODEL?

[Andrei Alexandrescu]

The druntime build uses MODEL in all of its command lines. However, when 
generating headers it does not generate them in MODEL-dependent directories.

I checked and the generated headers are identical regardless of MODEL. 
Should we assume that at least in the future the generated imports may 
depend on MODEL? If so, we need to generate them in MODEL-dependent 
directories. Otherwise, we shouldn't pass MODEL in the respective 
command line.


Andrei