FindBoost: Add note about header-only libs in warning msg
It seems users run into this from time to time (#19609, #19606 (closed)), the added note may help.
Topic-rename: FindBoost-clarify-header-only
It seems users run into this from time to time (#19609, #19606 (closed)), the added note may help.
Topic-rename: FindBoost-clarify-header-only