RFR: JDK-8305414: gtest/NMTGtests.java is failing various sub-tests [v6]

[Thomas Stuefe]

> With [JDK-8304815](https://bugs.openjdk.org/browse/JDK-8304815) we started to use NMT - if enabled - for better hs-err reporting by asking it to make sense out of otherwise unknown memory locations.
> 
> If the location points into or nearby a C-heap block, we now see that. That even works for dead blocks (use after free). For details, see JDK-8304815 and the comments in mallocTracker.cpp.
> 
> The change came with its own gtest, which promptly started to fail on some platforms. The reason was an error in MallocTracker::print_pointer_information() that caused us to prematurely return from its search-loop if we encounter unmapped memory. Never happened in my tests, but of course depends on where libc places the test blocks, which makes this error intermittent.
> 
> Patch fixes that, and also fixes some debug output in the test.
> 
> Tests: Ran the test manually on Linux aarch64; was able to reproduce the errors without patch, no errors with patch.

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  Update comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13296/files
  - new: https://git.openjdk.org/jdk/pull/13296/files/613d38a4..68ea5b74

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13296&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13296&range=04-05

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13296.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13296/head:pull/13296

PR: https://git.openjdk.org/jdk/pull/13296