atomic: Solaris needs the _nv variant of atomic_or_uint.

(This means "new value" and returns the atomically updated value. Before, we
were returning a value from a void function.)

(cherry picked from commit 498cbffd89105efbcdb5b79fa1478cdf91fbc351)

src/atomic/SDL_atomic.c

@@ -257,7 +257,7 @@ int SDL_AtomicGet(SDL_AtomicInt *a)
 #elif defined(SDL_PLATFORM_MACOS) /* this is deprecated in 10.12 sdk; favor gcc atomics. */
     return sizeof(a->value) == sizeof(uint32_t) ? OSAtomicOr32Barrier(0, (volatile uint32_t *)&a->value) : OSAtomicAdd64Barrier(0, (volatile int64_t *)&a->value);
 #elif defined(SDL_PLATFORM_SOLARIS)
-    return atomic_or_uint((volatile uint_t *)&a->value, 0);
+    return atomic_or_uint_nv((volatile uint_t *)&a->value, 0);
 #else
     int value;
     do {