Document using local fypp/fortuno

[bhourahine]

Also change fortuno finder and version requirement to be able to use the debian fypp 3.1 install via command line cmake flag -DFETCHCONTENT_SOURCE_DIR_FYPP=/usr/bin

[fpenunuri]

@bhourahine,
Thanks for this useful update. However, when testing the build, I ran into two issues:

1. Fortuno subproject fetch error
   CMake failed during the update step with the error:

   Failed to get the hash for HEAD
   

   This occurred because I cloned the main project using SSH (git@github.com:...) but the Fortuno subproject is fetched over HTTPS by default.

   In mixed SSH/HTTPS setups, Git authentication can silently fail when used inside FetchContent.

   I resolved this by adding a DNAOAD_USE_SSH CMake option to switch the repository URL to SSH (git@github.com:...) when needed. This allows consistent protocol use across both main and subprojects, especially helpful when credentials are SSH-based.

2. Fortran compiler compatibility issue
   When compiling Fortuno with gfortran 11.4 (Ubuntu 22.04), I encountered the following error:

   stop exitcode, quiet=.true.
                     1
   Error: Syntax error in STOP statement at (1)
   

   (file: _build/_deps/fortuno-src/src/fortuno_serial/serialcmdapp.f90:36:18)

   This is valid Fortran 2008 syntax, and gfortran ≥10 is supposed to support it, but the error persists.
   The build succeeded when using Intel's ifx compiler, which handles the quiet argument correctly.

As for fypp.cmake, I didn’t encounter any issues.

[bhourahine]

@fpenunuri for the DNAOAD_USE_SSH could you confirm which version of cmake you use (I suspect it is 3.22, by v 3.28 the https address resolves for mixed SSH/HTTPS)?

Point 2 is seems to be a known compiler bug from the 11.4 and earlier releases:
https://gcc.gnu.org/pipermail/gcc-bugs/2022-February/778732.html

[fpenunuri]

@bhourahine Thanks for confirming. Yes, I’m currently using CMake 3.22.
Also, thanks for the link regarding the compiler bug — that clarifies point 2.