[Cin] shared build fix for my Slackware

[Andrea paz]

> Can you confirm
> --without-thirdparty --disable-libdpx --without-libdpx --without-lv2 --disable-static-build
> also still works?
>
I don't know if my test has any value, since I did it on 64-bit Arch.
However the build with patching and disabling thirdparty, etc gave no
errors and some simple editing test showed no problems.
The only errors involved loading OpenCL plugins:

build plugin index for: /home/paz/cinelerra5/cinelerra-5.1/bin/plugins
PluginFFilter::new_ffilter(overlay_opencl)
  err: Input/output error
PluginFFilter::new_ffilter(overlay_qsv)
  err: Input/output error
PluginFFilter::new_ffilter(program_opencl)
  err: Operation not permitted
PluginFFilter::new_ffilter(remap_opencl)
  err: Input/output error
PluginFFilter::new_ffilter(xfade_opencl)
  err: Input/output error
[openclsrc_883 @ 0x55c0871a9940] OpenCL source requires output
dimensions to be specified.
PluginFFilter::new_ffilter(openclsrc)
  err: Invalid argument
build ladspa plugin index for: /home/paz/cinelerra5/cinelerra-5.1/bin/ladspa

But they do not affect the operation of CinGG. I attach the logs if
they are of interest.
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