In 1.7.0 we introduced CMake config files, which make it easy for CMake-based projects to find libbson's and libmongoc's header and library paths. The Debian package does not include these files however:

/usr/lib/x86_64-linux-gnu/cmake/libbson-1.0/libbson-1.0-config-version.cmake
/usr/lib/x86_64-linux-gnu/cmake/libbson-1.0/libbson-1.0-config.cmake
/usr/lib/x86_64-linux-gnu/cmake/libmongoc-1.0/libmongoc-1.0-config-version.cmake
/usr/lib/x86_64-linux-gnu/cmake/libmongoc-1.0/libmongoc-1.0-config.cmake