RFR: 8279998: PPC64 debug builds fail with "untested: RangeCheckStub: predicate_failed_trap_id"

[Aleksey Shipilev]

Current mainline fails bootcycle-images build with hitting the `__ untested` assertion. Looking at how other platforms implemented the same block, I think PPC64 code is the same, and we are more or less safe with just dropping that assertion.

Attention @GoeLin.

Additional testing:
 - [x] Linux ppc64le fastdebug, `make bootcycle-images` (now passes)
 - [ ] Linux ppc64le fastdebug, `tier1`
 - [ ] Linux ppc64le fastdebug, `tier2`

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/7077/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7077&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279998
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7077.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7077/head:pull/7077

PR: https://git.openjdk.java.net/jdk/pull/7077