dovecot 2.2.31: linking error

[Rupert Gallagher]

-std=gnu99
-mmacosx-version-min=10.12
[...]
Undefined symbols for architecture x86_64:
"_imapc_client_cmd", referenced from:
_imapc_quota_refresh in quota-imapc.o
"_imapc_client_get_capabilities", referenced from:
_imapc_quota_refresh in quota-imapc.o
"_imapc_command_sendf", referenced from:
_imapc_quota_refresh in quota-imapc.o
"_imapc_simple_callback", referenced from:
_imapc_quota_refresh in quota-imapc.o
"_imapc_simple_context_init", referenced from:
_imapc_quota_refresh in quota-imapc.o
"_imapc_simple_run", referenced from:
_imapc_quota_refresh in quota-imapc.o
"_imapc_storage_client_register_untagged", referenced from:
_imapc_quota_refresh in quota-imapc.o
ld: symbol(s) not found for architecture x86_64
clang-4.0: error: linker command failed with exit code 1 (use -v to see invocation)