Fix compilation error in tutorials for linux

[feniksa]

GLTF library contains implicit dependency from openmp. Latest gcc version doesn't include openmp by default, so it is requried to bypass -fopenmp flag for linker

This commit fix compilation of:

• 60_mesh_export
• 61_mesh_import

  RadeonProRender/binUbuntu18/libProRenderGLTF.so: undefined reference to `omp_get_thread_num'
  RadeonProRender/binUbuntu18/libProRenderGLTF.so: undefined reference to `omp_get_num_threads'
  RadeonProRender/binUbuntu18/libProRenderGLTF.so: undefined reference to `omp_get_thread_num'
  RadeonProRender/binUbuntu18/libProRenderGLTF.so: undefined reference to `omp_get_num_threads'
  RadeonProRender/binUbuntu18/libProRenderGLTF.so: undefined reference to `GOMP_parallel'
  RadeonProRender/binUbuntu18/libProRenderGLTF.so: undefined reference to `GOMP_parallel'

:Testing Performed: Compiled and run at gentoo linux