RFR: 8278479: RunThese test failure with +UseHeavyMonitors and +VerifyHeavyMonitors [v2]

[Coleen Phillimore]

> This change adds a null check before calling into Runtime1::monitorenter when -XX:+UseHeavyMonitors is set. There's a null check in the C2 and interpreter code before calling the runtime function but not C1.
> 
> Tested with tier1-7 (a little of 8) and built on most non-oracle platforms as well.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Improve c1 code.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9339/files
  - new: https://git.openjdk.org/jdk/pull/9339/files/912dc5cd..116e2b5a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9339&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9339&range=00-01

  Stats: 12 lines in 6 files changed: 0 ins; 6 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/9339.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9339/head:pull/9339

PR: https://git.openjdk.org/jdk/pull/9339