Impossible to know for sure without more details on how you built ICU. It is possible libicuuc.so is just an alias and it requires the actual library file at libicuuc.so.67.1 or similar.
The guide you are reading is very old and probably out of date. However, I can vouch for this succeeding. The details of each step can be found in the neighbouring directory. If you are working with the 5.3.3 release instead of the development state of Swift, look in the toolchain‐5.3 branch instead.