--build-path option creates a {sketch_path} file instead

[usr97629238]

That commandline arduino-cli -v compile --fqbn ATTinyCore:avr:attinyx5 attiny85.ino --build-path ./build/ --output-dir ./firmware/ works fine with other cores, like digistump:avr:digispark-tiny, but with ATTinyCore the build files still go in the temporary folder and it creates a ./{sketch_path} file instead.