Allow `provision.sh` to use embedded GCC and ignore system installed version

[rikkuness]

I have arm-none-eabi-gcc installed from system packages so the provision.sh ofc warns:

===== ARM
arm-none-eabi-gcc installed, version 14.2.0
*********************************************************************
*********************************************************************
***                                                               ***
*** ARM GCC IS INSTALLED ALREADY, BUT IS NOT THE EXPECTED VERSION ***
***                                                               ***
***   The build may work with your compiler version, but it       ***
***   is possible you will encounter errors, or issues with       ***
***   build size                                                  ***
***                                                               ***
*********************************************************************
*********************************************************************
      Expected 13.2.1
      Got      14.2.0

I would prefer to use the embedded version so versions match up. It'd be neat to have an env var that allows skipping the check for the existence in the PATH and then installs gcc-arm-embedded anyway. Then when it updates the PATH with the path to the extracted version, put it at the start of PATH instead of the end so that it takes preference over the system version.