[jdk11u-dev] RFR: 8297951: C2: Create skeleton predicates for all If nodes in loop predication

[Goetz Lindenmaier]

I backport this for parity with 11.0.19-oracle.

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Commit messages:
 - Backport 0bd04a658963c1126faa776cb8a96c23beb5e3e6

Changes: https://git.openjdk.org/jdk11u-dev/pull/1686/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1686&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297951
  Stats: 85 lines in 2 files changed: 78 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1686.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1686/head:pull/1686

PR: https://git.openjdk.org/jdk11u-dev/pull/1686