Toolchain coupling with GCC

[Carldkennedy]

As it stands, the Bessemer documentation looks coherent on coupling with the toolchain GCC versioning so there's nothing to fix there.

That said I think a compromise here would be to make an import highlighting the importance of matching then, amend both pages at the same time with the import. That sounds like another PR.

Originally posted by @jkwmoore in https://github.com/rcgsheffield/sheffield_hpc/pull/1659#discussion_r1135623441