Build controls for AIX with xlclang and openxl toolchains

[tjcw]

Proposed changes

Supply build controls for AIX xlclang and openxl toolchains

Types of changes

What types of changes does your code introduce?

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Documentation content changes
• Other (please describe):

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I searched the discussions
• I searched the closed and open issues
• I read the contribution guidelines
• I added myself to the copyright attributions for significant changes
• I checked that tests pass locally with my changes
• I added tests that prove my fix is effective or that my feature works
• I added necessary documentation (if appropriate)

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...