Their symbol was the eight-pointed Chaos star altered to make a Moorcock weep, its diagonal arms bent fylfot, a swastika that pointed in all directions.
He's referring to the eight-armed symbol of Chaos used in the Elric novels. The fylfot or fylfot cross, tho, is a real thing, it's another word for swastika. The generally accepted etymology is simply fill-foot, as in a design to fill the foot of a painted window. The OED provides this citation from the Landsdowne manuscripts:
Let me stand in the medyll pane..a rolle abo[ve my hede] in the hyest..[pane] vpward, the fylfot in the nedermast pane vnder ther I knele
The OED notes that it might have been a nonce word in this citation, a word created for this particular purpose.
In French the design is cramponné "cramped", in German it's Hakenkreuz "hooked cross", and in Greek it's γαμμάτιον/γαμμάδιον (gammadion) because it's formed from the letter Γ gamma. In Sanskrit, svastika means "lucky or auspicious object".