Fix a bug in dependency generation
Vamsi Vytla:
In file 'dep_solver.py': f._dep_fixed is set when
get/set_dep_requires/provides are invoked. Suppose, the variable
'_dep_fixed' for 'file_2.v' gets set in the invocation of
'_create_deps()' during the call '_lookup_post_provider()' for
'file_1.v', then the solver never gets a chance to set the post
provider for 'file_2.v' before 'file_2.v' in the fset.