RFR: 8289856: [PPC64] SIGSEGV in C2Compiler::init_c2_runtime() after JDK-8289060 [v3]

[Martin Doerr]

> We're currently calling `nullptr->is_valid()` and `nullptr->value()` which causes SIGSEGV on PPC64 (and is undefined behavior). See JBS for details.

Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:

  Revert whitespace change.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9403/files
  - new: https://git.openjdk.org/jdk/pull/9403/files/58cefd26..a11a20c9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9403&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9403&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9403.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9403/head:pull/9403

PR: https://git.openjdk.org/jdk/pull/9403