SW4STM32 - use GCC v4.9 ?
I found this article - which is how GNU ARM Eclipse recommends handling it:
http://gnuarmeclipse.github.io/toolchain/path/
Sadly, the options they point to are not present in SW4STM32!
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Development tools for Zephyr on STM32
Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.
Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.