opencv3: build against native SDKs, do not force 10.7 SDK which breaks powerpc builds

[barracuda156]

The port unnecessarily forces 10.7 SDK on 10.6 and earlier, which obviously cannot work for PowerPC and apparently unjustified for x86. At least for the default variant: the port has numerous variants, so it is possible that some of those in fact require 10.7+ SDK, but then the requirement should be placed accordingly.

This is the only fix needed on 10.6 (it was needed for much earlier versions already, hence the date):

--- modules/videoio/CMakeLists.txt	2015-12-18 23:02:16.000000000 +0800
+++ modules/videoio/CMakeLists.txt	2024-07-15 04:48:46.000000000 +0800
@@ -144,9 +144,6 @@
   if(UNIX AND BZIP2_LIBRARIES)
     list(APPEND VIDEOIO_LIBRARIES ${BZIP2_LIBRARIES})
   endif()
-  if(APPLE)
-    list(APPEND VIDEOIO_LIBRARIES "-framework VideoDecodeAcceleration" bz2)
-  endif()
 endif(HAVE_FFMPEG)
 
 if(HAVE_PVAPI)

(On 10.6 ppc I had to build against libdispatch-legacy, which is not needed on x86, and likely not needed on 10.5, though I cannot test that at the moment.)