[MacPorts] #62847: opencv4: fix build failures for MacOS 10.7 and 10.8

[MacPorts]

#62847: opencv4: fix build failures for MacOS 10.7 and 10.8
---------------------+----------------------
 Reporter:  mascguy  |      Owner:  mascguy
     Type:  defect   |     Status:  assigned
 Priority:  Normal   |  Milestone:
Component:  ports    |    Version:
 Keywords:           |       Port:  opencv4
---------------------+----------------------
 When compiling `opencv4` for MacOS 10.7 and 10.8, the following
 compilation error occurs:

 {{{
 In file included from
 /opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_graphics_opencv4/opencv4/work/opencv-4.5.2/modules/imgcodecs/src/apple_conversions.mm:5:
 In file included from
 /opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_graphics_opencv4/opencv4/work/opencv-4.5.2/modules/imgcodecs/src/apple_conversions.h:6:
 In file included from
 /System/Library/Frameworks/Accelerate.framework/Headers/Accelerate.h:20:
 In file included from
 /System/Library/Frameworks/vecLib.framework/Headers/vecLib.h:69:
 /System/Library/Frameworks/vecLib.framework/Headers/vForce.h:31:19: error:
 reference to 'complex' is ambiguous
         template<> class complex<float>;
                          ^
 /System/Library/Frameworks/vecLib.framework/Headers/vForce.h:30:26: note:
 candidate found by name lookup is 'std::complex'
         template<class T> class complex;
                                 ^
 /opt/local/libexec/llvm-9.0/bin/../include/c++/v1/complex:261:28: note:
 candidate found by name lookup is 'std::__1::complex'
 class _LIBCPP_TEMPLATE_VIS complex
                            ^
 }}}

 I believe this issue started occurring with OpenCV releases > 4.3.0.

 Since this port used to build successfully for MacOS releases as old as
 10.7, we should fix this if possible.

-- 
Ticket URL: <https://trac.macports.org/ticket/62847>
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