I can tell you WHAT this error is, but not how to fix it :(
3dDespike is written to use the OpenMP parallelizing system for speed -- that is, it runs in multiple threads. The binary version of AFNI you have installed must be compiled to use OpenMP using gcc. "libgomp" is "library gcc OpenMP" -- but that is not installed on your computer.
Fixing this requires either (a) using a version of Linux that supports OpenMP, or (b) installing AFNI binaries that do not use OpenMP -- which will be slower. I guess that you are using one of the "linux_openmp" binaries -- to check, type the command 'afni --ver'. You could try installing one of the "linux_xorg7" binaries instead. However, using OpenMP will make various AFNI programs run faster (that's the point of OpenMP), so it would be better to use a Linux version/gcc installation that supports OpenMP. But I can't tell you how to do that.
