RFR: 8352163: [AIX] SIGILL in AttachOperation::ReplyWriter::write_fully after 8319055

[Alex Menkov]

The change fixes crash on AIX after JDK-8319055
Can't test it on AIX, but the reason is obvious from the stack trace.
AIX is the only platform that does not implement `reply_writer` yet

Testing: sanity tier1

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jdk/pull/24089/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24089&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8352163
  Stats: 5 lines in 1 file changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/24089.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24089/head:pull/24089

PR: https://git.openjdk.org/jdk/pull/24089