After extracting sources archive we have these SQL files for each engine:

data.sql
double.sql
history_pk_prepare.sql
images.sql
schema.sql

After we run "make clean", only these are left:

double.sql
images.sql

And its not possible to get those all SQL files back except of extracting the archive again.
"dbschema" target is commented out in generated Makefile, not sure why it's so, so we cannot run"make dbschema" as well.

It's unexpected and not user friendly.