fix dependency of include files under learn/building_programs mini-book

[p-costa]

I had to do this fix to the dependencies generator, to be able to build a project in the case when the makefile is not in the same directory as the source files. I hope this makes sense!

[p-costa]

(I just noticed that I accidentally did not fork the project... I hope this is fine, else I can close and re-submit a proper PR)

[awvwgk]

Nice catch.

If you are on it already, could you mend the regex above to also include zeros? [a-zA-Z][a-zA-Z0-9_] instead of [a-zA-Z][a-zA-Z1-9_]?

[awvwgk]

I'm surprised this is actually used, I wrote this guide to show how involved the makefile setup can become and motivate people to use fpm or other high-level build systems with proper Fortran support ;).

[p-costa]

I'm surprised this is actually used, I wrote this guide to show how involved the makefile setup can become and motivate people to use fpm or other high-level build systems with proper Fortran support ;).

fpm will come first for me! But I also want to update my naive build workflow using make with this nice and robust one.