devel/cligen: fix build on GCC architectures

In file included from cligen_object.c:63:
cligen_object.h:98: error: redefinition of typedef 'parse_tree'
cligen_parsetree.h:53: error: previous declaration of 'parse_tree' was here
cligen_object.h:187: error: redefinition of typedef 'cg_obj'
cligen_parsetree.h:51: error: previous declaration of 'cg_obj' was here