When you compile qt from source without having gperf installed, it still starts to compile WebEngine, but then fails inside WebKits CSS name generator, due to a FileNotFound exception in Python.

Installing gperf was more a lucky guess on my side after that vague error message (I saw, that parameter --gperf was passed to the script and guessed that gperf might be the file it couldn't find).

We should test gperf presence at configure time and fail with a better error message if it is missing.