RFR: 8288687: (fc) Unix version ofFileChannelImpl.transferTo0() should should return IOS_UNSUPPORTED if not Linux, macOS, nor AIX

[Brian Burkhalter]

Return `IOS_UNSUPPORTED` from the `#else` conditional compilation branch of `Java_sun_nio_ch_FileChannelImpl_transferTo0`.

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Commit messages:
 - 8288687: (fc) Unix version ofFileChannelImpl.transferTo0() should should return IOS_UNSUPPORTED if not Linux, macOS, nor AIX

Changes: https://git.openjdk.org/jdk/pull/9205/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9205&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288687
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9205.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9205/head:pull/9205

PR: https://git.openjdk.org/jdk/pull/9205