brew.sh: define minimum required Glibc version

[maxim-belkin]

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Define minimum required Glibc version in one central location -- brew.sh

[BrewTestBot]

Review period will end on 2020-12-17 at 23:46:28 UTC.

[MikeMcQuaid]

Thanks @maxim-belkin! Looking good, just had some ideas on making this robust to future refactoring.

[MikeMcQuaid]

👏🏻 Perfect, thanks @maxim-belkin!

[maxim-belkin]

Thanks for the review, Mike!

[BrewTestBot]

Review period ended.

[sjackman]

Thanks, Maxim!