simplify build systesm
simplify build systesm

stdlib.rake takes MFACTOR_DEFINING_OBJECT, which should be set by the host
application to the object file that depends on the generated source files.
`stdlib.rake` takes care of setting the dependencies.
Supersedes non-functional _generated_ pseudofile dependency.

timor/mfactor,timor/mfactor,timor/mfactor,timor/mfactor