RFR: Copy powershell script in make build as well

[Jorn Vernee]

I noticed that the powershell script we added is only being copied to the output directory as part of the gradle build. This PR makes it so we also copy it in the make build.

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Commit messages:
 - copy ps1 script in make build

Changes: https://git.openjdk.org/jextract/pull/260/files
  Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=260&range=00
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jextract/pull/260.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/260/head:pull/260

PR: https://git.openjdk.org/jextract/pull/260