graphics/librtprocess: fix build without libomp
CMake Error at /usr/local/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
Could NOT find OpenMP_CXX (missing: OpenMP_CXX_FLAGS OpenMP_CXX_LIB_NAMES)
Call Stack (most recent call first):
/usr/local/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE) /usr/local/share/cmake/Modules/FindOpenMP.cmake:596 (find_package_handle_standard_args) src/CMakeLists.txt:4 (find_package)