package/opencv: fix opencv.pc generation

This change fixes build of packages depending on opencv and using
pkg-config to get the opencv LDFLAGS, which were wrongly ordered for
static build and included absolute path pointing to the host system
libraries instead of the sysroot ones.

This patch fixes build issues with gst1-plugins-bad and vlc.

This change introduce and new patch to opencv, which is already merged
upstream [1].

Fixes:
  http://autobuild.buildroot.net/results/c70/c70f793c7c3b380428d6e2e622a90805cffc4dd1/
  ... and many others

[1] https://github.com/Itseez/opencv/commit/eceada586bbf18fc267e437522ec4f1f23ddc656

Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/opencv/0003-cmake-OpenCVGenPkgconfig.cmake-rework-opencv.pc-gene.patch

@@ -0,0 +1,156 @@
+From eceada586bbf18fc267e437522ec4f1f23ddc656 Mon Sep 17 00:00:00 2001
+From: Samuel Martin <s.martin49@gmail.com>
+Date: Fri, 3 Oct 2014 00:32:40 +0200
+Subject: [PATCH] cmake/OpenCVGenPkgconfig.cmake: rework opencv.pc generation
+
+Using absolute path to locate the components in the "Libs:" field of the
+*.pc can badly break cross-compilation, especially when building
+statically linked objects.
+
+Indeed, pkg-config automatically replaces the '-I...' and '-L...' paths
+when the PKG_CONFIG_SYSROOT_DIR and PKG_CONFIG_LIBDIR environment
+variables are set [1]. This feature is very helpful and common in
+cross-compilation framework like Buildroot [2,3].
+
+When there are absolute paths in the *.pc files, pkg-config won't be
+able to do the path substitions for these paths when the afromentioned
+environment variables are set.
+In such case, since the prefix is the target one, not the sysroot one,
+these libraries' abolute paths will point to:
+- in the best case: a non-existing file (i.e. these files do not exists
+  on the host system;
+- at worst: the host system's libraries. This will make the linking
+  failed because these host system's libraries will most likely not be
+  build for the target architecture [4].
+
+So, this patch replace the components' absolute paths by the form:
+  -L<libdir> -l<libname>
+
+This way, the linker will be able to resolve each dependency path,
+whatever the kind of objects/build (shared object or static build) it
+is dealing with.
+
+Note that for static link, the library order does matter [5]. The order
+of the opencv components has been carefully chosen to comply with this
+requirement.
+
+Fixes #3931
+
+[1] http://linux.die.net/man/1/pkg-config
+[2] http://buildroot.org/
+[3] http://git.buildroot.net/buildroot/tree/package/pkgconf/pkg-config.in
+[4] http://autobuild.buildroot.net/results/e8a/e8a859276db34aff87ef181b0cce98916b0afc90/build-end.log
+[5] http://stackoverflow.com/questions/45135/linker-order-gcc
+
+Signed-off-by: Samuel Martin <s.martin49@gmail.com>
+
+---
+Note: this patch properly applies on top of the master branch, though it
+      has been written on top of the 2.4 branch.
+---
+ cmake/OpenCVGenPkgconfig.cmake | 64 +++++++++++++++++++++++++++---------------
+ 1 file changed, 42 insertions(+), 22 deletions(-)
+
+diff --git a/cmake/OpenCVGenPkgconfig.cmake b/cmake/OpenCVGenPkgconfig.cmake
+index fa57db9..183c56d 100644
+--- a/cmake/OpenCVGenPkgconfig.cmake
++++ b/cmake/OpenCVGenPkgconfig.cmake
+@@ -8,10 +8,6 @@
+ #
+ # ${BIN_DIR}/unix-install/opencv.pc -> For use *with* "make install"
+ # -------------------------------------------------------------------------------------------
+-set(prefix      "${CMAKE_INSTALL_PREFIX}")
+-set(exec_prefix "\${prefix}")
+-set(libdir      "") #TODO: need link paths for OpenCV_EXTRA_COMPONENTS
+-set(includedir  "\${prefix}/${OPENCV_INCLUDE_INSTALL_PATH}")
+ 
+ if(CMAKE_BUILD_TYPE MATCHES "Release")
+   set(ocv_optkind OPT)
+@@ -35,42 +31,66 @@ ocv_list_reverse(OpenCV_LIB_COMPONENTS)
+ ocv_list_reverse(OpenCV_EXTRA_COMPONENTS)
+ 
+ #build the list of components
+-set(OpenCV_LIB_COMPONENTS_ "")
+-foreach(CVLib ${OpenCV_LIB_COMPONENTS})
+-  get_target_property(libpath ${CVLib} LOCATION_${CMAKE_BUILD_TYPE})
+-  get_filename_component(libname "${libpath}" NAME)
+ 
+-  if(INSTALL_TO_MANGLED_PATHS)
+-    set(libname "${libname}.${OPENCV_VERSION}")
+-  endif()
++# Note:
++#   when linking against static libraries, if libfoo depends on libbar, then
++#   libfoo must come first in the linker flags.
++
++# world is a special target whose library should come first, especially for
++# static link.
++if(OpenCV_LIB_COMPONENTS MATCHES "opencv_world")
++  list(REMOVE_ITEM OpenCV_LIB_COMPONENTS "opencv_world")
++  list(INSERT OpenCV_LIB_COMPONENTS 0 "opencv_world")
++endif()
++
++set(OpenCV_LIB_COMPONENTS_)
++foreach(CVLib ${OpenCV_LIB_COMPONENTS})
+ 
+-  #need better solution....
+-  if(libpath MATCHES "3rdparty")
+-    set(installDir "share/OpenCV/3rdparty/${OPENCV_LIB_INSTALL_PATH}")
++  get_target_property(libloc ${CVLib} LOCATION_${CMAKE_BUILD_TYPE})
++  if(libloc MATCHES "3rdparty")
++    set(libpath "\${exec_prefix}/share/OpenCV/3rdparty/${OPENCV_LIB_INSTALL_PATH}")
+   else()
+-    set(installDir "${OPENCV_LIB_INSTALL_PATH}")
++    set(libpath "\${exec_prefix}/${OPENCV_LIB_INSTALL_PATH}")
+   endif()
++  list(APPEND OpenCV_LIB_COMPONENTS_ "-L${libpath}")
++
++  get_filename_component(libname ${CVLib} NAME_WE)
++  string(REGEX REPLACE "^lib" "" libname "${libname}")
++  list(APPEND OpenCV_LIB_COMPONENTS_ "-l${libname}")
+ 
+-  set(OpenCV_LIB_COMPONENTS_ "${OpenCV_LIB_COMPONENTS_} \${exec_prefix}/${installDir}/${libname}")
+ endforeach()
+ 
+ # add extra dependencies required for OpenCV
+-set(OpenCV_LIB_COMPONENTS ${OpenCV_LIB_COMPONENTS_})
+ if(OpenCV_EXTRA_COMPONENTS)
+   foreach(extra_component ${OpenCV_EXTRA_COMPONENTS})
+ 
+-    if(extra_component MATCHES "^-[lL]" OR extra_component MATCHES "[\\/]")
+-      set(maybe_l_prefix "")
++    if(extra_component MATCHES "^-[lL]")
++      set(libprefix "")
++      set(libname "${extra_component}")
++    elseif(extra_component MATCHES "[\\/]")
++      get_filename_component(libdir "${extra_component}" PATH)
++      list(APPEND OpenCV_LIB_COMPONENTS_ "-L${libdir}")
++      get_filename_component(libname "${extra_component}" NAME_WE)
++      string(REGEX REPLACE "^lib" "" libname "${libname}")
++      set(libprefix "-l")
+     else()
+-      set(maybe_l_prefix "-l")
++      set(libprefix "-l")
++      set(libname "${extra_component}")
+     endif()
+-
+-    set(OpenCV_LIB_COMPONENTS "${OpenCV_LIB_COMPONENTS} ${maybe_l_prefix}${extra_component}")
++    list(APPEND OpenCV_LIB_COMPONENTS_ "${libprefix}${libname}")
+ 
+   endforeach()
+ endif()
+ 
++list(REMOVE_DUPLICATES OpenCV_LIB_COMPONENTS_)
++string(REPLACE ";" " " OpenCV_LIB_COMPONENTS "${OpenCV_LIB_COMPONENTS_}")
++
+ #generate the .pc file
++set(prefix      "${CMAKE_INSTALL_PREFIX}")
++set(exec_prefix "\${prefix}")
++set(libdir      "\${exec_prefix}/${OPENCV_LIB_INSTALL_PATH}")
++set(includedir  "\${prefix}/${OPENCV_INCLUDE_INSTALL_PATH}")
++
+ if(INSTALL_TO_MANGLED_PATHS)
+   set(OPENCV_PC_FILE_NAME "opencv-${OPENCV_VERSION}.pc")
+ else()
+-- 
+2.4.1
+