subr_rangeset.c is the only source file that calls functions like pctrie_insert and pctrie_remove directly; other users of pctries use the PCTRIE_DEFINE macro to define interfaces to pctrie that let them ignore issues of offsets within structs and uint64_t return values.

Change subr_rangeset.c to use PCTRIE_DEFINE too. And change pctrie.h to mark the lookup function as unused, to avoid warnings when compiling files, like subr_rangeset.c, that don't invoke lookup().

I can compile and boot a kernel. I don't know that I've actually tested rangesets in doing that, though.