[jdk17u-dev] RFR: 8292072: NMT: repurpose Tracking overhead counter as global malloc counter

[Goetz Lindenmaier]

A useful improvement to NMT. Applied clean, but
to compile, I had to move malloc_overhead() behind the decl of MallocHeader.

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Depends on: https://git.openjdk.org/jdk17u-dev/pull/1820

Commit messages:
 - Backport 1c1c4410b20f598c7e81fae044b6cb298ed12bab

Changes: https://git.openjdk.org/jdk17u-dev/pull/1821/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1821&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292072
  Stats: 56 lines in 4 files changed: 13 ins; 32 del; 11 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1821.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1821/head:pull/1821

PR: https://git.openjdk.org/jdk17u-dev/pull/1821