We recently switched to using the v4 toolchain. The v3 reference in the test/build code is spread at various places. Some of these are not obvious, eg: WT-10505, where compatibility tests use a script to build various WiredTiger versions instead of code in evergreen yml files. This makes it hard to switch to a new toolchain.

WT-10506 adds "stable" toolchain cmake files that redirect to the latest toolchain (v4 at the moment). We will switch to using the stable toolchain for all build tasks. This way it will be easier to upgrade the toolchains the next time by just pointing the stable cmake to the latest one.