RFR: 8313368: (fc) FileChannel.size returns 0 on block special files

[Brian Burkhalter]

Reinstate header files so that `BLKGETSIZE64` is defined on Linux.

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

Commit messages:
 - 8313368: (fc) FileChannel.size returns 0 on block special files

Changes: https://git.openjdk.org/jdk/pull/15092/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15092&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313368
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15092.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15092/head:pull/15092

PR: https://git.openjdk.org/jdk/pull/15092