[jdk11u-dev] RFR: 8289856: [PPC64] SIGSEGV in C2Compiler::init_c2_runtime() after JDK-8289060

[Martin Doerr]

Clean backport of JDK-8289856 (except Copyright year update). Avoids undefined behavior.

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Commit messages:
 - Backport e05b2f2c3b9b0276099766bc38a55ff835c989e1

Changes: https://git.openjdk.org/jdk11u-dev/pull/1205/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1205&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289856
  Stats: 65 lines in 1 file changed: 0 ins; 0 del; 65 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1205.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1205/head:pull/1205

PR: https://git.openjdk.org/jdk11u-dev/pull/1205