[Ninja] Fix build system self-destructing on clean
List generated files including CMAKE_CURRENT_BINARY_DIR
in
DUNE_INSTANCE_GENERATED
. This means we do not need to set the source file
property GENERATED
on the generated files, which is only meant for files
generated during build time (e.g. with add_custom_command()
or during
generate time (e.g. with file(GENERATE)
).
Closes: #119 (closed)