RFR: 8295414: [Aarch64] C2: assert(false) failed: bad AD file

[Dean Long]

The "bad AD file" error is because PartialSubtypeCheck produces an iRegP_R5 result, which cannot be matched as an input where iRegP is expected.
Update the test to reproduce the crash and updated iRegP rule to match iRegP_R5.
The fact that this went so long without being noticed makes me wonder how much test coverage PartialSubtypeCheck has received on aarch64.

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Commit messages:
 - update test
 - match iRegP_R5 as iRegP

Changes: https://git.openjdk.org/jdk/pull/10749/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10749&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295414
  Stats: 5 lines in 2 files changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10749.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10749/head:pull/10749

PR: https://git.openjdk.org/jdk/pull/10749