Add function walkKernelM for no-op traversal over Kernel.
Add function walkKernelM for no-op traversal over Kernel.

ihc/futhark,HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,ihc/futhark,diku-dk/futhark,ihc/futhark,HIPERFIT/futhark,diku-dk/futhark,HIPERFIT/futhark