[foreign-jextract] RFR: The test LibUnsupportedTest fails on Linux

[Athijegannathan Sundararajan]

-l unsupported -> -l Unsupported

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Commit messages:
 - The test LibUnsupportedTest fails on Linux

Changes: https://git.openjdk.java.net/panama-foreign/pull/411/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=411&range=00
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/411.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/411/head:pull/411

PR: https://git.openjdk.java.net/panama-foreign/pull/411