[PostGIS] #6134: visual examples can't be built if sfcgal is not enabled

[PostGIS]

#6134: visual examples can't be built if sfcgal is not enabled
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  Reporter:  strk     |      Owner:  strk
      Type:  defect   |     Status:  new
  Priority:  blocker  |  Milestone:  PostGIS 3.7.0
 Component:  build    |    Version:  master
Resolution:           |   Keywords:
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Comment (by robe):

 Should we disable docs for sections where you don't build e.g. if sfcgal
 is not enabled makes sense you wouldn't need sfcgal docs right?
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/6134#comment:1>
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