fts: improve memory-allocation errno handling * lib/fts.c (fts_read, fts_build): When enter_dir or setup_dir fails, report its errno value back to the user. (internal_function): Preserve errno. * modules/fts (Depends-on): Add calloc-posix, free-posix, malloc-posix, and realloc-posix, for better errno handling on allocation failures.