Enkkidu Glamdring only converts flat "Added" Melee damage, that means "increased" melee damage affixes do not work. So every 3 flat melee damage you get is converted to spell damage for Frost Claw. Keep in mind flat damage of a corresponding element (i.e. melee fire damage) would not be useful since even though it is converted to spell damage for Frost Claw, it is converted to Spell FIRE damage which is an element we do not scale.