For historical reasons, we have not been defining NDEBUG globally in the server build. This resulted in at least one subtle misconfiguration (see SERVER-11010). We fixed SERVER-11010 by adding NDEBUG, but scoped only to the gperftools build, but this won't protect against other future third_party dependencies on NDEBUG.

We should, early in 2.7, promote NDEBUG to the top level build for non-debug builds.