[Bug fortran/78822] [cleanup] replace static char buffers by std:string

[janus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78822

--- Comment #5 from janus at gcc dot gnu.org ---
Created attachment 40346
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40346&action=edit
draft patch

Here is a draft patch that implements what I had in mind (regtests cleanly).