Minor change to CMake: move the -Werror stuff to top level

Might as well centralize things like this, since we don't want warnings anywhere.

I also once accidentally migrated a package and put the -Werror into Athena, people did not like that. Won't happen again if it's in the top level CMake list.

@svanstro this is pretty minor, any objections?

approved this merge request

added 2 commits

• f8f3edea - 1 commit from branch atlas-flavor-tagging-tools:main
• 989020cf - move the -Werror stuff to top level

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enabled an automatic merge when all merge checks for 989020cf pass

merged