RFR: 8236569: -Xss not multiple of 4K does not work for the main thread on macOS

[Adam Sotona]

This is continuation of PR #4256 

The patch simply rounds up the specified stack size to multiple of the system page size, on systems where necessary.
The patch is based on the original PR/branch, with reflected remaining recommendations.

Please review.

Thank you,
Adam

-------------

Commit messages:
 - puting EINVAL on the RHS of the == as recommended
 - Update help text
 - Cast type
 - Change java -X output for -Xss
 - Only try to round-up when current value failed
 - Avoid overflow on page size
 - JDK-8236569: -Xss not multiple of 4K does not work for the main thread on macOS

Changes: https://git.openjdk.java.net/jdk/pull/8953/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8953&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8236569
  Stats: 41 lines in 3 files changed: 39 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8953.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8953/head:pull/8953

PR: https://git.openjdk.java.net/jdk/pull/8953