[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 #14 from janus at gcc dot gnu.org ---
Created attachment 40350
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40350&action=edit
patch using build_message_string

So here is another patch, similar to the one in comment 5, but using
build_message_string instead of std::string.

Apparently this works pretty nicely as well (at least it regtests cleanly).
Regarding readability, I'd say it's a matter of taste (and what you're used
to).

One advantage of the std::string version is obviously that it cleans up after
itself and one doesn't need to free up things manually. But in general I'm
still not sure how well it plays along with GCC's ideas of memory management.