This repo compile teensy 3.5 core with gcc-arm-7-2017-q4.
sudo apt install meson ninja-build
meson build --cross-file teensy-3.5-cross.txt
cd build
ninja
Look blink example for teensy with meson :
https://github.com/leroilion/teensy-blink
https://github.com/PaulStoffregen/cores.git
Teensy 2.0, 3.x, LC core libraries for Arduino.
The latest stable version of Teensy's core library is always available in the Teensyduino installer, at this page: