I did not see an answer for this, so here is what I think it should be...
You change the toolchain using the main toolbar, called "Build Configuration / Toolchain" -- Do not use the menu on Build Settings. That just changes the settings for the specified toolchain; it does not select a toolchain.
If you cannot see the main toolbar in PSoC Creator, right-click next to another toolbar to access the different toolbars available.
Finally, under the Tools menu select Options, and point to Project Management > Generic Toolchains. This is where you tell PSoC Creator where the toolchain is.
Hope this helps!
toolchain_selection.jpg 78.1 K