[jdk11u-dev] RFR: 8241004: NMT tests fail on unaligned thread size with debug build

[Ahmed Muhsin]

Backport of [JDK-8241004](https://bugs.openjdk.java.net/browse/JDK-8241004). Applies cleanly.

This is will prevent hotspot runtime/NMT test failures on mac-aarch64. See issue 2 in this comment for more context: https://github.com/openjdk/jdk11u-dev/pull/715#issuecomment-1020401252

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Commit messages:
 - Backport 0b20eafb30cc1de372141f2a427d13fdc6565e3a

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/812/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=812&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8241004
  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/812.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/812/head:pull/812

PR: https://git.openjdk.java.net/jdk11u-dev/pull/812