The 1st printing of Dieties & Demigods contained the Cthulhu mythos, until Arkham (? or whoever controlled the rights to HPL's works at the time) threatened legal action.
Chaosium owned the gaming rights to both Elric and Cthulhu, which is why subequent printings of D&Demi ommitted references to those works.
IIRC, rather than threaten lawsuits and send our C&D notices, the two companies simply worked out an agreement, whereby Chaosium would be allowed to use some TSR trademarks in their Thieves World game.