RFR: 8294578: [PPC64] C2: Missing is_oop information when using disjoint compressed oops mode

[Martin Doerr]

Fix missing is_oop information shown by assertion `assert(t->base() == Type::Int || t->base() == Type::Half || t->base() == Type::FloatCon || t->base() == Type::FloatBot) failed: Unexpected type`. See JBS issue for details.

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Commit messages:
 - 8294578: [PPC64] C2: Missing is_oop information when using disjoint compressed oops mode

Changes: https://git.openjdk.org/jdk/pull/10484/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10484&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294578
  Stats: 6 lines in 1 file changed: 5 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10484.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10484/head:pull/10484

PR: https://git.openjdk.org/jdk/pull/10484