How to write a gtk-fortran application that can be used with or without GUI

[vmagnin]

@Jweber

When looking at the current LICENSE file in the gtk-fortran GitHub repository, there is a copy of GPL 3, but no reference to the GCC Runtime Library Exception.

Thanks @Jweber for pointing this problem. The GCC Runtime Library Exception was chosen with the GPLv3 since the beginning of the project in 2011 (see for example Issue #24). And it is written in the header of the source files.

I will look how to fix the omission with @JerryD. I don’t know if we should copy the GCC Runtime Library Exception text into the LICENSE file, or if we should add a second file with that text.

(and I don’t think GitHub can handle that in its metada)