Compiling C sources

Hello,

I'm compiling a project which has some C sources besides the Ada ones. 
I've set up the project with both languages checked, set the C switches 
and so on.

Now, I find that when building the project the C sources aren't 
compiled, so the final link fails because of some missing symbols. If I 
manually open these files, compile, and add pragma Linker_Options to 
include its object files, everything works.

I've tried manually editing the project file to add the Source_Files 
property adding only the C files. Doing so the remaining Ada sources are 
no longer counted in the project. So I suppose this could work, but then 
I ought to add manually all project files to this list. ?

So, I suspect I'm missing the proper easy way to automatize this, but I 
don't find it in the GPS documentation. Any ideas?

Kind regards,

A. Mosteo.