Pullup ticket #6352 - requested by nia
graphics/openexr: NetBSD 8 build fix

Revisions pulled up:
- graphics/openexr/buildlink3.mk                                1.16

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  Module Name: pkgsrc
  Committed By: nia
  Date: Sun Oct 18 09:52:32 UTC 2020

  Modified Files:
  pkgsrc/graphics/openexr: buildlink3.mk

  Log Message:
  openexr: Require at least gcc6 in dependent packages

  (attempt to fix dependent packages in NetBSD 8.x)

(bsiegert)