Keep the prl files around when building Qt
Keep the prl files around when building Qt

Summary: This is useful for cmake builds.

Test Plan:
  make -C ../depends/ build-all

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1807

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