Symbian build system
It gather info of sources to build from module.mk. This applied for new build system aka python package symbian_builder and old build system aka BuildPackageUpload_AllVersions.pl and BuildPackageUpload_LocalSettings.pl.
Old was dumb and hard to maintain.
New build system gather info from configure.engine too. It auto generates symbian project files for all supported engines, exclude unfinished engines and subengines from release build. Main advantage - it builds in parallel and even errors can't interrupt while all engine not processed.
Anyone free to add and remove files which doesn't use Symbian API directly.