[foreign-jextract] RFR: 8240373: Jextract assigns type "Void" to enum macros

[Athijegannathan Sundararajan]

This has been fixed in the new jextract code. Adding a test.

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Commit messages:
 - 8240373: Jextract assigns type "Void" to enum macros

Changes: https://git.openjdk.java.net/panama-foreign/pull/446/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=446&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8240373
  Stats: 60 lines in 2 files changed: 58 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/446.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/446/head:pull/446

PR: https://git.openjdk.java.net/panama-foreign/pull/446