RFR: 8229147: Linux os::create_thread() overcounts guardpage size with newer glibc (>=2.27)

[David Holmes]

We can now detect whether glibc includes the guard pages as part of the requested stack size or not, and so only need to make adjustments when glibc requires it.

The intent was to use a local variable as the "flag" but unfortunately it is also needed in os_posix.cpp so I had to make it part of the os::Linux API.

See bug report (and related) for details.

Testing:
  - Manually checked log output for stack sizes and boundaries on systems with and without the glibc fix. (Again see JBS issue)
  -  Tiers 1-3 sanity
Thanks

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Commit messages:
 - Remove testing log output
 - 8229147: Linux os::create_thread() overcounts guardpage size with newer glibc (>=2.27)

Changes: https://git.openjdk.org/jdk/pull/13571/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13571&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8229147
  Stats: 71 lines in 3 files changed: 39 ins; 13 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/13571.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13571/head:pull/13571

PR: https://git.openjdk.org/jdk/pull/13571