Write your own 'make clean'

Compiling Octopus on the HPC, strange core dump on attempting to compile & an odd ‘error #7013: This module file was not generated by any release of this compiler.’ found buried in ./configure’s config.log from Intel’s Fortran compiler. Turned out to be stale object files from a previous interation of getting it to compile; lesson learned - if there’s no ‘make clean’, write your own!