Need to figure out:
What time is used to build llvm
What time is used to build gotollvm
Klee builds about 5 minutes if llvm is installed
LLVM builds about several hours
gotollvm builds also about several hours
In UTBotCpp simple llvm build is provided with ready to use docker image, which is a great way
https://github.com/UnitTestBot/UTBotCpp/pkgs/container/utbotcpp%2Fbase_env
Also maybe some llvm libs can be downloaded with apt without building llvm
Use this guide to build llvm with less pain https://github.com/Software-Analysis-Team/UnitTestFuzzerCPP/wiki/Сборка-clang-llvm
Maybe klee docker can be used or other simple procedures to install kleee https://klee.github.io/getting-started/