Unlined, definitely! My wife wears these all day, every day. They form the spine of her "retired in south Florida" wardrobe. Every time she buys another pair, I just tell her they would work very nicely on Camino. She has not yet done one, but, I am cleverly working behind the scenes so she has the clothing to be good-to-go!
You will heat up and perspire as you walk during the day. Lined pants, of any sort, would be too warm, IMHO. Plus, as you will be doing hand washing more often than not, you want pants, again of any type, that will rinse out easier and dry faster. Consider that in May and June, many of the places you will stay are rather chilly and damp all night. Outside clothes drying on lines is not always possible because of overnight showers or early morning ground fog.
In my experience, most albergues and many hostals are stingy with their heat, as it adds cost, and not value, when seen from their perspective. You usually, if lucky, get a blast around 21:00 - 22:00, and again at 05:00 to maybe 06:00. The former is to facilitate bathing, changing and getting ready to sleep. The latter is to facilitate your getting the heck out of the albergue or hostal and onto the Camino again in the morning.
I hope this helps.