[jdk21u-dev] RFR: 8327114: Attach in Linux may have wrong behaviour when pid == ns_pid (Kubernetes debug container)

[Goetz Lindenmaier]

I backport this for parity with 21.0.11-oracle.

Clean backport, but needed to adapt syntax.

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Commit messages:
 - fix build
 - backport 52ba72823be0c969ab873ead2863ec48f883210b

Changes: https://git.openjdk.org/jdk21u-dev/pull/2523/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2523&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327114
  Stats: 218 lines in 2 files changed: 143 ins; 8 del; 67 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2523.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2523/head:pull/2523

PR: https://git.openjdk.org/jdk21u-dev/pull/2523