RFR: 8271471: [IR Framework] Rare occurrence of "<!-- safepoint while printing -->" in PrintIdeal/PrintOptoAssembly can let tests fail

[Christian Hagedorn]

A test VM used by the IR framework sometimes prints `` in the middle of emitting a `PrintIdeal` or `PrintOptoAssembly` output which could lead to IR matching failures:
https://github.com/openjdk/jdk/blob/489e5fd12a37a45f4f5ea64b05f85c6f99f70811/src/hotspot/share/utilities/ostream.cpp#L918-L927

I thought about just bailing out of IR matching if this string is found after a failure but this issue also affects internal framework tests (I observed one case locally where this happened in the test `TestIRMatching`, letting it fail).

Handling `` makes things more complicated for the IR framework tests. I'm not sure about the value of printing this message in the first place. But if nobody objects, I suggest to either remove it or at least guard it with `Verbose`, for example. I went with the latter solution in this PR.

Thanks,
Christian

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Commit messages:
 - 8271471: [IR Framework] Rare occurrence of "<!-- safepoint while printing -->" in PrintIdeal/PrintOptoAssembly can let tests fai

Changes: https://git.openjdk.java.net/jdk/pull/4932/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4932&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271471
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4932.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4932/head:pull/4932

PR: https://git.openjdk.java.net/jdk/pull/4932