In libmongoc-1.0.pc the Libs line is

Libs: -lsasl2 -framework Security -framework CoreFoundation  -L${libdir} -lmongoc-1.0

Some systems or tool chains process libaries in order and only link used functions. For such systems the order of the libraries is significant. Since mongoc-1.0 depends on the other libraries, this ordering might be better:

Libs: -L${libdir} -lmongoc-1.0  -lsasl2 -framework Security -framework CoreFoundation 

I've had to edit the pc file manually recently to get a project to build properly.
I've been using r1.3. The file appears to be unchanged through recent master 26494954a.

Thanks.