RFR: 8268103: JNI functions incorrectly return a double after JDK-8265836

[Severin Gehwolf]

Please review this trivial patch.  Stubs should return `-1` for `jlong` rather than `-1.0` (`double`) on aix/macosx.

Thoughts?

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Commit messages:
 - 8268103: JNI functions incorrectly return a double after JDK-8265836

Changes: https://git.openjdk.java.net/jdk/pull/4300/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4300&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268103
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4300.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4300/head:pull/4300

PR: https://git.openjdk.java.net/jdk/pull/4300