augustus: don't hardcode gcc version

[alebcay]

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Did not bump revision because #{Formula["gcc"].version_suffix} should resolve to 9 right now anyways.

Related to #54364.

[DesWurstes]

Isn't this better? (For consistency too)

with_env("HOMEBREW_CC" => Formula["gcc"].opt_bin/"gcc-#{Formula["gcc"].version_suffix}") 

[alebcay]

You're right, that is more consistent with where it's used in some other places in Homebrew.

[BrewTestBot]

🤖 A scheduled task has triggered a merge.