Arch Linux: problems building opencv with cuda; libopencv_core.so.3.4.0: undefined reference to `cblas_dgemm'

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I am currently trying to build a version of opencv, featuring cuda, on my arch linux computer. For that, I use opencv-cuda-git as base version. Additionally, I modified the PKGBUILD and added additional flags to further adapt opencv to my system.

However, everytime I run the buildprocess (makepkg csri), it fails with following error message:

[ 16%] Building CXX object modules/hdf/CMakeFiles/example_hdf_create_groups.dir/samples/create_groups.cpp.o
cd /home/tobias/builds/opencv-cuda-git/src/opencv/build/modules/hdf && /usr/bin/cmake -E cmake_link_script CMakeFiles/example_hdf_create_groups.dir/link.txt --verbose=1
/bin/g++-6  -std=c++11   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffast-math -ffunction-sections -fdata-sections  -msse -msse2 -fvisibility=hidden -fvisibility-inlines-hidden -Wno-invalid-offsetof -O3 -DNDEBUG  -DNDEBUG  -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now  -Wl,--gc-sections   -rdynamic CMakeFiles/example_hdf_create_groups.dir/samples/create_groups.cpp.o  -o ../../bin/example_hdf_create_groups  -L/opt/cuda/lib64 ../../lib/libopencv_hdf.so.3.4.0 ../../lib/libopencv_highgui.so.3.4.0 ../../lib/libopencv_videoio.so.3.4.0 ../../lib/libopencv_imgcodecs.so.3.4.0 ../../lib/libopencv_imgproc.so.3.4.0 ../../lib/libopencv_core.so.3.4.0 ../../lib/libopencv_cudev.so.3.4.0 
../../lib/libopencv_core.so.3.4.0: undefined reference to `cblas_zgemm'
../../lib/libopencv_core.so.3.4.0: undefined reference to `cblas_sgemm'
../../lib/libopencv_core.so.3.4.0: undefined reference to `cblas_dgemm'
../../lib/libopencv_core.so.3.4.0: undefined reference to `cblas_cgemm'
make[2]: *** [modules/hdf/CMakeFiles/example_hdf_create_groups.dir/build.make:102: bin/example_hdf_create_groups] Error 1
make[2]: Leaving directory '/home/tobias/builds/opencv-cuda-git/src/opencv/build'
make[1]: *** [CMakeFiles/Makefile2:2523: modules/hdf/CMakeFiles/example_hdf_create_groups.dir/all] Error 2
make[1]: Leaving directory '/home/tobias/builds/opencv-cuda-git/src/opencv/build'
make: *** [Makefile:163: all] Error 2

My previous search suggested that this error might occur due to a linking error with cublas. Therefore I tried to add -L/opt/cuda/lib64 and -lcublas to CMAKE_CXX_FLAGS. That made no difference at all.

Suggestions by another blog contained using gcc-6 instead of g++-6. That however yields another error:

[ 16%] Linking CXX executable ../../bin/example_hdf_create_groups
cd /home/tobias/builds/opencv-cuda-git/src/opencv/build/modules/hdf && /usr/bin/cmake -E cmake_link_script CMakeFiles/example_hdf_create_groups.dir/link.txt --verbose=1
/bin/gcc-6  -std=c++11   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffast-math -ffunction-sections -fdata-sections  -msse -msse2 -fvisibility=hidden -fvisibility-inlines-hidden -Wno-invalid-offsetof -O3 -DNDEBUG  -DNDEBUG  -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now  -Wl,--gc-sections   -rdynamic CMakeFiles/example_hdf_create_groups.dir/samples/create_groups.cpp.o  -o ../../bin/example_hdf_create_groups  -L/opt/cuda/lib64 ../../lib/libopencv_hdf.so.3.4.0 ../../lib/libopencv_highgui.so.3.4.0 ../../lib/libopencv_videoio.so.3.4.0 ../../lib/libopencv_imgcodecs.so.3.4.0 ../../lib/libopencv_imgproc.so.3.4.0 ../../lib/libopencv_core.so.3.4.0 ../../lib/libopencv_cudev.so.3.4.0     
ld: CMakeFiles/example_hdf_create_groups.dir/samples/create_groups.cpp ...