[jdk11u-dev] RFR: 8223140: Clean-up in 'ok_to_convert()'

[Goetz Lindenmaier]

I downport this for parity with 11.0.134-oracle.

Applied clean except for patch to debug.hpp. Those macros were already downported.

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Commit messages:
 - Backport f4faee7bae5bdfcae994e95dc7e4e53ba850db98

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/463/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=463&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8223140
  Stats: 52 lines in 3 files changed: 15 ins; 13 del; 24 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/463.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/463/head:pull/463

PR: https://git.openjdk.java.net/jdk11u-dev/pull/463