RFR: 8361433: [Big Endian] assert(verify_guards()) failed: Expected valid memory guards after 8357601 [v2]

[Martin Doerr]

> Big Endian fix for [JDK-8357601](https://bugs.openjdk.org/browse/JDK-8357601).
> 
> Note: The first commit is only a Big Endian fix. The code looks still wrong for platforms which don't support unaligned accesses. Also see `UseUnalignedAccesses`.
> The second commit changes to check `os::is_readable_range()`.

Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:

  Use os::is_readable_range().

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26140/files
  - new: https://git.openjdk.org/jdk/pull/26140/files/ced69858..2f467b3a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26140&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26140&range=00-01

  Stats: 10 lines in 1 file changed: 5 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26140.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26140/head:pull/26140

PR: https://git.openjdk.org/jdk/pull/26140