Hide or fix all build warnings

[corey-derochie-amd]

Details

Do not mention proprietary info or link to internal work items in this PR.

Work item: "Internal", or link to GitHub issue (if applicable).

What were the changes?

• Ignore variable-length arrays warnings (clang compiler supports as an extension but gives a warning)
• Fixed some const-correctness in unit tests

Why were the changes made?
Compile warnings are problematic.

Approval Checklist

Do not approve until these items are satisfied.

• [ ] Verify the CHANGELOG has been updated, if
  • there are any NCCL API version changes,
  • any changes impact library users, and/or
  • any changes impact any other ROCm library.