I'm not sure that's a minor one in the case of Fortran, I've seen enough Fortran code to know that every codebase has its own special set of flags that it needs

I'm not sure that's a minor one in the case of Fortran, I've seen enough Fortran code to know that every codebase has its own special set of flags that it needs to compile correctly (or the need to dig up an old, unmaintained compiler...). Also missing from the Fortran code is `implicit none` (and let's not talk about good old fixed format or the mess with comparison operators or common blocks or ...).