RFR: 8343137: C2: VerifyLoopOptimizations fails with "Was reachable in only one"

[Christian Hagedorn]

[JDK-8342043](https://bugs.openjdk.org/browse/JDK-8342043) introduced a new usage of `igvn.intcon()` but missed to call `set_ctrl()`. This simple patch fixes this.

While working on this, I've noticed that a few Assertion Predicates tests ended up in the `predicates` directory while they would have better been placed into `predicates/assertion`. It's probably not worth to file a separate issue just for that, so I've squeezed this trivial move into this fix. Note that `AssertionPredicateDoesntConstantFold` does not define a package and thus does not need an update to the command line.

Thanks,
Christian

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Commit messages:
 - 8343137: C2: VerifyLoopOptimizations fails with "Was reachable in only one"

Changes: https://git.openjdk.org/jdk/pull/21739/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21739&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343137
  Stats: 234 lines in 6 files changed: 145 ins; 85 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/21739.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21739/head:pull/21739

PR: https://git.openjdk.org/jdk/pull/21739