[Buildroot] [PATCH] package/opencv3: allow to use pkg-config while cross-compiling

[Peter Korsgaard]

>>>>> "Romain" == Romain Naour <romain.naour at smile.fr> writes:

 > Since version 3.4.1 [1], opencv disable pkg-config while cross-compiling to
 > avoid host headers/libraries poisoning.

 > Due to this, opencv fail to detect ffmpeg, gstreamer and gtk dependencies
 > even if	the corresponding support is requested by
 > BR2_PACKAGE_OPENCV3_WITH_{FFMPEG,GSTREAMER,GTK2,GTK3}.

 > Maybe other dependencies are affected by this issue...

 > While configuring opencv we can notice the following messages:
 > "-- OpenCV disables pkg-config to avoid using of host libraries. Consider using PKG_CONFIG_LIBDIR to specify target SYSROOT"
 > "-- Can't find ffmpeg - 'pkg-config' utility is missing"

 > As the result ffmpeg and gstreamer are not enabled:
 > --   Video I/O:
 > --     FFMPEG:                      NO
 > --       avcodec:                   NO
 > --       avformat:                  NO
 > --       avutil:                    NO
 > --       swscale:                   NO
 > --       avresample:                NO
 > --     GStreamer:                   NO
 > --     libv4l/libv4l2:              NO
 > --     v4l/v4l2:                    linux/videodev2.h

 > We can fixes this by adding a new option OPENCV_ENABLE_PKG_CONFIG=ON

 > --   Video I/O:
 > --     FFMPEG:                      YES
 > --       avcodec:                   YES (ver 58.35.100)
 > --       avformat:                  YES (ver 58.20.100)
 > --       avutil:                    YES (ver 56.22.100)
 > --       swscale:                   YES (ver 5.3.100)
 > --       avresample:                YES (ver 4.0.0)
 > --     GStreamer:
 > --       base:                      YES (ver 1.16.0)
 > --       video:                     YES (ver 1.16.0)
 > --       app:                       YES (ver 1.16.0)
 > --       riff:                      YES (ver 1.16.0)
 > --       pbutils:                   YES (ver 1.16.0)
 > --     libv4l/libv4l2:              NO
 > --     v4l/v4l2:                    linux/videodev2.h

 > Add host-pkgconf in the dependencies.

 > If there is a path poisoning issue, it will be detected by the toolchain
 > paranoid wrapper.

 > [1] https://github.com/opencv/opencv/commit/c4f9ff0285130bd8bcf9d87a9ea6949bdd7e9e5d

 > Signed-off-by: Romain Naour <romain.naour at smile.fr>
 > Cc: Samuel Martin <s.martin49 at gmail.com>
 > Cc: Fabrice Fontaine <fontaine.fabrice at gmail.com>
 > Cc: Bernd Kuhls <bernd.kuhls at t-online.de>
 > ---
 > This patch should be backported to Buildroot 2019.02 that use opencv 3.4.2.

Committed to 2019.02.x and 2019.05.x, thanks.

-- 
Bye, Peter Korsgaard