RFR: 8291569: Consider removing JNI checks for signals SIGPIPE and SIGXFSZ

[David Holmes]

Simple enhancement to skip checking of the handlers for SIGPIPE and SIGXFSZ as we really don't care if they change, and we expect that they can.

The signal checking code might seem to have a redundancy as we skip these signals in two places, but the primary use of the `do_check_signal_periodically` array is to allow for only issuing one warning per signal. I could have skipped them in either place and get the same effect but it seemed inappropriate to set the array entry and not do the check; and vice-versa.

Testing: just basic sanity test tiers 1-3. This doesn't affect any application behaviour.

There are no regression tests in this specific area and it did not seem worth the effort creating one just for this.

Thanks.

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Commit messages:
 - 8291569: Consider removing JNI checks for signals SIGPIPE and SIGXFSZ

Changes: https://git.openjdk.org/jdk/pull/12062/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12062&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291569
  Stats: 13 lines in 1 file changed: 9 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12062.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12062/head:pull/12062

PR: https://git.openjdk.org/jdk/pull/12062