I'm encountering a linker error consuming a libmongoc static library I built through Xcode:
https://groups.google.com/forum/#!topic/mongodb-user/E7qkt9con3A

I was able to replicate the exact linker error outside of Xcode, using the library's own build system. The error occurs when I build just the static library, and not the dylib.

```
./autogen.sh
./configure --with-libbson=no --enable-ssl=no --enable-sasl=no --disable-shared --enable-static && make
```

The static library seems to be missing the non-extern declarations for the counter types, and the linker errors arise when building the tests:

```
CC tests/test_secondary-test-secondary.o
CC tests/test_secondary-mongoc-tests.o
CCLD test-secondary
clang: warning: argument unused during compilation: '-pthread'
Undefined symbols for architecture x86_64:
"___mongoc_counter_auth_failure", referenced from:
__mongoc_cluster_auth_node in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_auth_success", referenced from:
__mongoc_cluster_auth_node in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_clients_active", referenced from:
_mongoc_client_new in libmongoc-priv.a(libmongoc_priv_la-mongoc-client.o)
_mongoc_client_destroy in libmongoc-priv.a(libmongoc_priv_la-mongoc-client.o)
"___mongoc_counter_clients_disposed", referenced from:
_mongoc_client_destroy in libmongoc-priv.a(libmongoc_priv_la-mongoc-client.o)
"___mongoc_counter_cursors_active", referenced from:
__mongoc_cursor_new in libmongoc-priv.a(libmongoc_priv_la-mongoc-cursor.o)
__mongoc_cursor_destroy in libmongoc-priv.a(libmongoc_priv_la-mongoc-cursor.o)
__mongoc_cursor_clone in libmongoc-priv.a(libmongoc_priv_la-mongoc-cursor.o)
"___mongoc_counter_cursors_disposed", referenced from:
__mongoc_cursor_destroy in libmongoc-priv.a(libmongoc_priv_la-mongoc-cursor.o)
"___mongoc_counter_dns_failure", referenced from:
_mongoc_client_default_stream_initiator in libmongoc-priv.a(libmongoc_priv_la-mongoc-client.o)
"___mongoc_counter_dns_success", referenced from:
_mongoc_client_default_stream_initiator in libmongoc-priv.a(libmongoc_priv_la-mongoc-client.o)
"___mongoc_counter_op_egress_delete", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_getmore", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_insert", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_killcursors", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_msg", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_query", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_reply", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_total", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_egress_update", referenced from:
__mongoc_cluster_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
__mongoc_cluster_try_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_delete", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_getmore", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_insert", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_killcursors", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_msg", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_query", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_reply", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_total", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_op_ingress_update", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_protocol_ingress_error", referenced from:
__mongoc_cluster_try_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-cluster.o)
"___mongoc_counter_streams_active", referenced from:
_mongoc_stream_buffered_new in libmongoc-priv.a(libmongoc_priv_la-mongoc-stream-buffered.o)
_mongoc_stream_buffered_destroy in libmongoc-priv.a(libmongoc_priv_la-mongoc-stream-buffered.o)
"___mongoc_counter_streams_disposed", referenced from:
_mongoc_stream_buffered_destroy in libmongoc-priv.a(libmongoc_priv_la-mongoc-stream-buffered.o)
"___mongoc_counter_streams_egress", referenced from:
_mongoc_socket_sendv in libmongoc-priv.a(libmongoc_priv_la-mongoc-socket.o)
"___mongoc_counter_streams_ingress", referenced from:
_mongoc_socket_recv in libmongoc-priv.a(libmongoc_priv_la-mongoc-socket.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```