Hadrian built stage1 compiler complains about missing `#define HS_CONSTANTS`

In the past I was able to run the stage0 compiler using a invocation like this:

_validatebuild/stage0/bin/ghc.exe ~/tmp/C.hs -O -fforce-recomp -package-db _validatebuild/stage0/lib/package.conf.d/

But that seems to have broken recently. I tried running the stage0 compiler manually today and got the above mentioned error. This is new and quite bothersome!