RFR: JDK-8296784: Provide clean mallinfo/mallinfo2 wrapper for Linux glibc platforms [v2]

[Thomas Stuefe]

> This is a breakout from [JDK-8293114](https://bugs.openjdk.org/browse/JDK-8293114), which is starved for reviews. So I attempt to break up that fix into smaller units which are hopefully easier to review separately.
> 
> We use the glibc-specific mallinfo/mallinfo2 APIs to query libc internals. These are quite important, since they are the only way to get the malloc load and retained size from the glibc allocator. NMT only reports a tiny part of that (only the user-view of whatever hotspot allocated).
> 
> Using these APIs and staying glibc-agnostic requires some twiddling. This patch provides a clean wrapper to hide that twiddling from the end caller.
> 
> Patch also fixes a display error that may have caused omission of the "may have wrapped" marker in the hs-err printout of the malloc load.
> 
> Also, gtest regression test.

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

  Feedback roman, martin

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/11088/files
  - new: https://git.openjdk.org/jdk/pull/11088/files/6dd6ec9b..ff26a182

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11088&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11088&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11088.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11088/head:pull/11088

PR: https://git.openjdk.org/jdk/pull/11088