(strtoimax): Guard declaration with `#if !HAVE_DECL_STRTOIMAX', rather than just `#ifndef strtoimax'. The latter fails because some systems (at least rs6000-ibm-aix4.3.3.0) have their own, conflicting declaration of strtoimax in sys/inttypes.h. (strtoumax): Likewise, for completeness (it wasn't necessary).