gwenbuild: Use existing build command list instead of creating an returning new ones.
Also allow to differentiate between error adding dependencies and simply empty dependency list (e.g. when requesting to build a file which is a non-generated source file).
gwenbuild: Use existing build command list instead of creating an returning new ones.
Also allow to differentiate between error adding dependencies and simply
empty dependency list (e.g. when requesting to build a file which is a
non-generated source file).