D alternative for C/C++ -Dfoo=42

[Cherry]

Just a few clarifications ....


> For now maybe I could keep an empty/default config.d somewhere 
> in the library source path.

I am creating a DSL (Domain Specific Language) library. I am 
talking about the library src path of my DSL library.

> And I could use that with multiple -J options. This way dmd 
> configuration from the default path unless it finds the config 
> file in the user path.
>

I figured that DMD will pick import file from the left-most -J 
path it finds the file in. So all I need is a wrapper over 
rdmd/dmd that adds a -J. and -J<default path> (in that order) to 
the user compile command.

Regards
- Cherry