unbound fails to rebuild

[Kastus Shchuka]

I have a strange problem rebuilding unbound after upgrade of libressl to 2.5.3.

Rebuild succeeded on one Yosemite system and fails on another with this error:

libtool: link: /usr/bin/clang -dynamiclib  -o .libs/libunbound.2.dylib  .libs/context.o .libs/libunbound.o .libs/libworker.o .libs/ub_event_pluggable.o .libs/dns.o .libs/infra.o .libs/rrset.o .libs/dname.o .libs/msgencode.o .libs/as112.o .libs/msgparse.o .libs/msgreply.o .libs/packed_rrset.o .libs/iterator.o .libs/iter_delegpt.o .libs/iter_donotq.o .libs/iter_fwd.o .libs/iter_hints.o .libs/iter_priv.o .libs/iter_resptype.o .libs/iter_scrub.o .libs/iter_utils.o .libs/localzone.o .libs/mesh.o .libs/modstack.o .libs/view.o .libs/outbound_list.o .libs/alloc.o .libs/config_file.o .libs/configlexer.o .libs/configparser.o .libs/fptr_wlist.o .libs/locks.o .libs/log.o .libs/mini_event.o .libs/module.o .libs/net_help.o .libs/random.o .libs/rbtree.o .libs/regional.o .libs/rtt.o .libs/dnstree.o .libs/lookup3.o .libs/lruhash.o .libs/slabhash.o .libs/timehist.o .libs/tube.o .libs/winsock_event.o .libs/autotrust.o .libs/val_anchor.o .libs/validator.o .libs/val_kcache.o .libs/val_kentry.o .libs/val_neg.o .libs/val_nsec3.o .libs/val_nsec.o .libs/val_secalgo.o .libs/val_sigcrypt.o .libs/val_utils.o .libs/dns64.o .libs/cachedb.o .libs/netevent.o .libs/listen_dnsport.o .libs/outside_network.o .libs/keyraw.o .libs/sbuffer.o .libs/wire2str.o .libs/parse.o .libs/parseutil.o .libs/rrdef.o .libs/str2wire.o .libs/strptime.o   -L/opt/local/lib -lssl -lcrypto  -Os -arch x86_64 -Wl,-headerpad_max_install_names -arch x86_64   -install_name  /opt/local/lib/libunbound.2.dylib -compatibility_version 7 -current_version 7.4 -Wl,-single_module -Wl,-exported_symbols_list,.libs/libunbound-symbols.expsym
Undefined symbols for architecture x86_64:
  "_ub_c_in", referenced from:
      _config_read in config_file.o
  "_ub_c_lex", referenced from:
      _ub_c_parse in configparser.o
  "_yywrap", referenced from:
      _yylex in configlexer.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [libunbound.la] Error 1

_yywrap exists in /opt/local/lib/libfl.dylib:

$ nm -gU /opt/local/lib/libfl.dylib
0000000000000f35 T _main
0000000000000f49 T _yywrap

Any ideas what I should check? 

Thanks,

Kastus