RFR: 8325621: Improve jspawnhelper version checks

[Chad Rakoczy]

Fix for [8325621](https://bugs.openjdk.org/browse/JDK-8325621)

Updates jspawnhelper to check that JDK version and jspawnhelper version are the same. Updates test to include check for version. Also tested manually by replacing jspawnhelper with incorrect version to confirm that check works.

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Commit messages:
 - Remove string.h include
 - Update test
 - Pass version as integer instead of string
 - Read in version using int instead of string
 - 8325621: Improve jspawnhelper version checks

Changes: https://git.openjdk.org/jdk/pull/18204/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18204&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325621
  Stats: 76 lines in 6 files changed: 70 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/18204.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18204/head:pull/18204

PR: https://git.openjdk.org/jdk/pull/18204