[foreign-jextract] RFR: 8252704: Absolute library paths are not properly quoted

[Jorn Vernee]

Hi,

This PR fixes a minor issue where backslashes (``) in absolute library paths result in un-compilable sources on Windows.

Thanks,
Jorn

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Commit messages:
 - Quote absolute library paths

Changes: https://git.openjdk.java.net/panama-foreign/pull/302/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=302&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252704
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/302.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/302/head:pull/302

PR: https://git.openjdk.java.net/panama-foreign/pull/302