extend/os/linux/system_config: show glibc/gcc version for API users

[cho-m]

• 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?

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I noticed that some issue reports showed N/A for glibc/etc even though Homebrew should have installed them.

Locally tried it out on Ubuntu 20.04 container and saw similar behavior, which seems due to API usage, e.g.

OS: Ubuntu 20.04.6 LTS
Host glibc: 2.31
/usr/bin/gcc: 9.4.0
/usr/bin/ruby: N/A
glibc: N/A
gcc@11: N/A
gcc: N/A
xorg: N/A

$ brew info glibc | grep Poured
  Poured from bottle using the formulae.brew.sh API on 2023-08-27 at 04:44:30

I think the original goal of conditional was to avoid auto-tapping homebrew/core, which I guess is only an issue now when API is disabled. May need confirmation that API logic will do what is expected.

Output with change:

OS: Ubuntu 20.04.6 LTS
Host glibc: 2.31
/usr/bin/gcc: 9.4.0
/usr/bin/ruby: N/A
glibc: 2.35_1
gcc@11: N/A
gcc: 13.1.0
xorg: N/A

[MikeMcQuaid]

Makes sense, thanks @cho-m!