[MacPorts] #70384: opencv3 fails to provide legacy module in contrib variant, which is required by digikam port

[MacPorts]

#70384: opencv3 fails to provide legacy module in contrib variant, which is
required by digikam port
--------------------------+------------------------------
 Reporter:  barracuda156  |      Owner:  mascguy
     Type:  defect        |     Status:  assigned
 Priority:  Normal        |  Milestone:
Component:  ports         |    Version:  2.9.3
 Keywords:                |       Port:  opencv3, digikam
--------------------------+------------------------------
 `digikam` expects `opencv` to have `legacy` module in `contrib`, but our
 port (3.4.16_19) do not build it at all:
 {{{
 -- First try at finding OpenCV...
 -- Could NOT find OpenCV (missing: contrib legacy) (found version
 "3.4.16")
 CMake Warning at core/cmake/modules/MacroOpenCV.cmake:27 (find_package):
   Found package configuration file:

     /opt/local/libexec/opencv3/cmake/OpenCVConfig.cmake

   but it set OpenCV_FOUND to FALSE so package "OpenCV" is considered to be
   NOT FOUND.
 }}}

 This makes it impossible to build. And unfortunately, `opencv` is a hard
 dependency (getting rid of it looks feasible but involving).

-- 
Ticket URL: <https://trac.macports.org/ticket/70384>
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