Function slurm_sys::slurmrs_free

#[no_mangle]
pub extern "C" fn slurmrs_free(ptr: *mut c_void)

This function can be passed as a callback to functions like slurm_list_create that want a deallocator argument. slurm_xfree doesn't work because (1) it takes a pointer to a pointer, so that it can zero it out; and (2) it takes additional arguments populated from C preprocessor __FILE__ and __LINE__ directives.