RFR: 8327621: Check return value of uname in os::get_host_name

[Johan Sjölen]

Hi,

Trivial bug fix where we didn't check the return value of `uname(2)` on POSIX platforms. I checked callers of `get_host_name` and all wrap the calls in an `if` branch so they already handle failures.

Regards,
Johan

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Commit messages:
 - Check the return value of uname

Changes: https://git.openjdk.org/jdk/pull/18157/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18157&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327621
  Stats: 5 lines in 1 file changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18157.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18157/head:pull/18157

PR: https://git.openjdk.org/jdk/pull/18157