Add the default target triple to match the target for the Windows
toolchain. This avoids the need for an additional parameter, and
it makes sense for the target to be the host by default. Explicit
parameters can change the target when desired.
The official builds include the profiling library, so we should enable
it on the CI to ensure that the path is tested. This should only add
~1m to the total build time.
This allows configuration of a build for just the runtime/SDK components
rather than a complete toolchain. It allows for more effective
iteration when working on just the runtime aspect of the toolchain.
