In my daily Archlinux setup I had issues compiling spectrumserver with opencl feature, It took me a few hours to find the solution...
All necessary packages were installed normally with the pacman package manager, up-to-date of course.
Except clFFT or clFFT-git installed using the AUR (https://aur.archlinux.org/) way
But many compilation errors around "c::" entries, apparently not declared so compilation just stop.
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The problem was an OpenCL API binding file, which was obsolete: opencl.hpp
If that can help people, the up-to-date file is available on github (https://github.com/KhronosGroup/OpenCL-CLHPP/blob/main/include/CL/opencl.hpp)
It has to be located in /usr/include/CL
You may also need clBLAS.h in /usr/include
PS: I'm using Nvidia GTX-970 video card in the machine running PhantomSDR-Plus
Regards
linkz