[jdk18] RFR: 8279370: jdk.jpackage/share/native/applauncher/JvmLauncher.cpp fails to build with GCC 6.3.0

[Aleksey Shipilev]

Seems like a missing include. C++ docs say `offsetof` is from `<cstddef>`, adding that include explicitly fixes the build. Seems to only happen with older GCCs, but it seems to be a happy accident it works on newer ones, probably through the transitive include somewhere.

Additional testing:
 - [x] Linux x86_64 fastdebug `tools/jpackage` tests
 - [x]  Linux x86_64 release `tools/jpackage` tests

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Commit messages:
 - Sort
 - Fix

Changes: https://git.openjdk.java.net/jdk18/pull/74/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=74&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279370
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/74.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/74/head:pull/74

PR: https://git.openjdk.java.net/jdk18/pull/74