[code-reflection] Integrated: More C99 code gen cleanup

[Gary Frost]

Just tidying up some C99 code gen. 

I added OpTk helpers and resused existing helper.

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Commit messages:
 - More C99 code gecn cleanup

Changes: https://git.openjdk.org/babylon/pull/730/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=730&range=00
  Stats: 147 lines in 4 files changed: 10 ins; 52 del; 85 mod
  Patch: https://git.openjdk.org/babylon/pull/730.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/730/head:pull/730

PR: https://git.openjdk.org/babylon/pull/730