Avoid using SSE in API when BT_USE_SSE_IN_API is not defined

Fixes Issue 683.

src/BulletCollision/CollisionShapes/btConvexShape.cpp

@@ -13,6 +13,10 @@ subject to the following restrictions:
 3. This notice may not be removed or altered from any source distribution.
 */
 
+#if defined (_WIN32) || defined (__i386__)
+#define BT_USE_SSE_IN_API
+#endif
+
 #include "btConvexShape.h"
 #include "btTriangleShape.h"
 #include "btSphereShape.h"