What is causing my error in executing arm-none-eabi-gcc.exe from Keil uVision?
I use Keil µVision, too (didn't even know you can set the GNU compiler)

I installed the "GNU Tools ARM Embedded\6 2017-q2-update" and Keil automatically filled the path - but without the leading /bin/ as seen in your screenshot. Maybe try removing it? (e.g. my path is "C:\Program Files (x86)\GNU Tools ARM Embedded\6 2017-q2-update\")