Memory Sanitizer requires all the dependencies, including
libstdc++ to be compiled with Memory Sanitizer, otherwise
we will get tons of false positives.
Run it in parallel with the old build system. This will offer
a migration path and make sure we keep everything working at
the cost of running many CI bots. New stuff is prefixed with "next".
Appveyor already got migrated to the next buildsystem.
After merging, we will follow-up removing duplicated core bots.
