RFR: Wrong libclang library name on Windows

[Jorn Vernee]

This snuck in when we recently refreshed the libclang bindings.

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Commit messages:
 - Use correct library name on Windows

Changes: https://git.openjdk.org/jextract/pull/172/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=172&range=00
  Stats: 3 lines in 1 file changed: 1 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/172.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/172/head:pull/172

PR: https://git.openjdk.org/jextract/pull/172