Testing locally, ENABLE_ICU=OFF (as specified in our docs here) results in linking errors. For example, the error:

/usr/bin/ld: /mongo-c-driver/src/libmongoc/src/mongoc/mongoc-scram.c:1065: undefined reference to `u_strFromUTF8_67'.

However, MONGOC_ENABLE_ICU=OFF compiles without issue but for some users (see CDRIVER-3915) this does not prevent libmongoc from linking against libicu.

We should investigate why the options above do not prevent libicu from linking.