Fix cppstd_compat migration for 2.12

[AbrilRBS]

Changelog: Bugfix: Avoid compatibility.py migration if any of the files are modified by users.
Docs: Omit

[AbrilRBS]

Hopefully I'm not missing anything

[jcar87]

warning if changes were made to that file

I may be missing this in the PR diff - but can't see in which situation / what warning is shown?

[memsharded]

I may be missing this in the PR diff - but can't see in which situation / what warning is shown?

There are no longer user changes that are not respected, so the warning is no longer necessary. That was intended for the initial case that the migration would be happening, without causing breakages, but some user custom changes to the cppstd_compat file only were not being used anymore. This no longer happens, and if the user has any changes to any of the files, they will always be respected.

[jcar87]

I may be missing this in the PR diff - but can't see in which situation / what warning is shown?

There are no longer user changes that are not respected, so the warning is no longer necessary. That was intended for the initial case that the migration would be happening, without causing breakages, but some user custom changes to the cppstd_compat file only were not being used anymore. This no longer happens, and if the user has any changes to any of the files, they will always be respected.

If pre-2.12 a user has modified either of the two files (even if one was modified and the other was still the original Conan one) - then a 2.12 upgrade will not touch any of the files?
This makes sense - just double checking