Building with the attached random configuration file,

mm/page_alloc.c: In function ‘early_page_uninitialised’:
mm/page_alloc.c:247:6: warning: unused variable ‘nid’ [-Wunused-variable]
  int nid = early_pfn_to_nid(pfn);
      ^
mm/page_alloc.c: In function ‘deferred_init_memmap’:
mm/page_alloc.c:1135:4: error: implicit declaration of function
‘meminit_pfn_in_nid’ [-Werror=implicit-function-declaration]
    if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
    ^