musl/arch/m68k/atomic_arch.h

#define a_cas a_cas
static inline int a_cas(volatile int *p, int t, int s)
{
	__asm__ __volatile__ (
		"cas.l %0, %2, (%1)"
		: "+d"(t) : "a"(p), "d"(s) : "memory", "cc");
	return t;
}