By simply changing how you are building Clipper1 you can avoid changes to it's related pri file:
wget https://sourceforge.net/projects/polyclipping/files/clipper_ver6.4.2.zip/download
unzip clipper_ver6.4.2.zip -d Clipper1
cd Clipper1/cpp
cmake -S . -B build -D CMAKE_INSTALL_PREFIX=../6.4.2
cmake --build ./build --target install
By simply changing how you are building Clipper1 you can avoid changes to it's related
prifile: