Currently in the compile mongodb task in evergreen.yml we compile MongoDB with the following command:

        ./buildscripts/scons.py --variables-files=etc/scons/mongodbtoolchain_stable_gcc.vars --link-model=dynamic --ninja generate-ninja ICECC=icecc CCACHE=ccache

However, in the Ninja Build Tool Setup and Use, etc/scons/mongodbtoolchain_stable_clang.vars is "recommended" instead. We should update this task to use clang