How to supress prompt on bc 5.3.1

[Masachika ISHIZUKA]

  I updated to master-n256084-5dd1f6f1441 (1400061) and this
leads to bc to 5.3.1.
  Previosly, 'BC-ENV-APRG=-P' or 'bc -P' were working but it
doesn't work on 5.3.1.  Is there any way to supress prompt ?
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Masachika ISHIZUKA