RFR: JDK-8282382: Report glibc malloc tunables in error reports

[Thomas Stuefe]

On Linux/glibc platforms, the hs-err file should report the malloc tunables, or at least MALLOC_ARENA_MAX, since that one can have a significant effect on footprint or malloc contention for a VM.

This patch adds this printout as a one-liner into hs-err files and jcmd VM.info reports:

Process Memory:                                                                    
...
glibc malloc tunables: MALLOC_PERTURB_=40, MALLOC_ARENA_MAX=1
If the tunables are default, we print glibc malloc tunables: (default).

Thanks, Thomas

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Commit messages:
 - report glibc malloc tunables

Changes: https://git.openjdk.java.net/jdk/pull/7620/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7620&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282382
  Stats: 33 lines in 1 file changed: 32 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7620.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7620/head:pull/7620

PR: https://git.openjdk.java.net/jdk/pull/7620