fix #9773, better error for trying to add a method to a non- generic …

…function

(cherry picked from commit 97381df)

src/toplevel.c

@@ -650,8 +650,7 @@ DLLEXPORT jl_value_t *jl_method_def(jl_sym_t *name, jl_value_t **bp, jl_binding_
  jl_value_t *gf=NULL;
 
  if (bnd && bnd->value != NULL && !bnd->constp) {
- jl_errorf("cannot define function %s; it already has a value",
- bnd->name->name);
+ jl_errorf("cannot define function %s; it already has a value", bnd->name->name);
  }
 
  if (*bp != NULL) {
@@ -662,7 +661,7 @@ DLLEXPORT jl_value_t *jl_method_def(jl_sym_t *name, jl_value_t **bp, jl_binding_
  jl_add_constructors((jl_datatype_t*)gf);
  }
  if (!jl_is_gf(gf)) {
- jl_error("invalid method definition: not a generic function");
+ jl_errorf("cannot define function %s; it already has a value", bnd->name->name);
  }
  }
  }