Draft: Add generated/ subdir to PROJECT_BINARY_DIR where dune-instance can put their generated files

Summary

It is not a good practice to include the full PROJECT_BINARY_DIR. This is currently necessary, since we generate file with dune-instance utilities in this directory, and also the config.h file is put into the binary-dir. While the issue with the config files is worked on, this MR moves all generated files into a subdirectory PROJECT_BINARY_DIR/generate to be included separately. Later we can remove the include of the base binary dir.

added buildsystem label

mentioned in merge request !1262 (merged)

My only concern is that this is yet another thing to teach people when solving #332 (closed). But this would only be a concern if we choose option (i) from #332 (closed).

This was just an experiment. Will be closed since it makes the handling of include directories not easier.

closed

mentioned in merge request !1355 (merged)

reopened