fix: solaris build support

[gaige]

What does this PR do?

The changes here are intended solely to add compatibility for builing on Solaris-based operating systems.
Changes are only to the build directives and thus will have no effect on other OS.

Why is it important?

In ordet to enable building beats for Solaris, Illumos, and SmartOS.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.md

Author's Checklist

• Ensure no negative effects on other OS

Related issues

• Fix SmartOS build issues (Solaris, Illumos) #249

[mauri870]

I saw your accompanying PR in Beats (elastic/beats#45105). Just to make sure we're on the same page: we don't have plans to support compiling to Solaris officially. This is purely community-driven work, and it may eventually break if users stop fixing issues.

That said, thanks for the effort on keeping the Solaris build working!

[mauri870]

/test

[mauri870]

/test

[gaige]

Thanks! Understood on the support side, but it’s super helpful not to have to maintain a fork :-)

For the time being, I’m interested in keeping things going. Maybe it’ll inspire some other SmartOS or Solaris folks to pitch in.