A typical use case for multiple configurations is that you have a release configuration (say `linux-x64`) and a debug configuration (say `linux-x64-debug`). You can now easily select the debug configuration with `CONF=debug`, or both configurations with `CONF=`, but there is no way to select just the release configuration. Instead, workarounds using `SPEC` or `CONF_NAME` (which always does an exact match) is needed.

Instead, we should modify the behavior of `CONF` slightly, so if it gets an exact match, it should behave like `CONF_NAME` and select just that configurations.