RFR: 8342769: gcc port broken on HotSpot

[Julian Waters]

Several areas in HotSpot are broken in the gcc port. These, with the exception of 1 rather big oversight withing SharedRuntime::frem and SharedRuntime::drem, are all minor correctness issues within the code. These mostly can be fixed with simple changes to the code. Note that I am not sure whether the SharedRuntime::frem and SharedRuntime::drem fix is correct. It may be that they can be removed entirely

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Commit messages:
 - 8342769

Changes: https://git.openjdk.org/jdk/pull/21627/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21627&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342769
  Stats: 69 lines in 6 files changed: 33 ins; 31 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/21627.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21627/head:pull/21627

PR: https://git.openjdk.org/jdk/pull/21627