• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

For most formulae, the bottles need a minimum libstdc++ rather than a minimum GCC version. This is particularly important when building on Ubuntu where the default compiler version is older than libstdc++.

So, checking the host libstdc++ version is a more accurate way to determine whether brew GCC is needed at runtime. This can be improved in the future to check symbol versions (e.g. GLIBCXX, CXXABI, GLIBC) which can allow some bottles to be installed even with older glibc/libstdc++.

This splits non-CI changes from #20609

Will add snippets of brew config on various Docker images below:

• rockylinux:9 (no system gcc)

  OS: Rocky Linux 9.3 (Blue Onyx)
  Host glibc: 2.34
  Host libstdc++: 6.0.29
  /usr/bin/gcc: N/A
  

• rockylinux:9 (with system gcc)

  OS: Rocky Linux 9.3 (Blue Onyx)
  Host glibc: 2.34
  Host libstdc++: 6.0.29
  /usr/bin/gcc: 11.5.0
  

• ubuntu:16.04 (no system gcc)

  OS: Ubuntu 16.04.7 LTS
  Host glibc: 2.23
  Host libstdc++: 6.0.21
  /usr/bin/gcc: N/A
  

• ubuntu:16.04 (with system gcc)

  OS: Ubuntu 16.04.7 LTS
  Host glibc: 2.23
  Host libstdc++: 6.0.21
  /usr/bin/gcc: 5.4.0