Make revolute joint actuation work properly even when SIMD is enabled.

src/dynamics/joint/fixed_joint.rs

@@ -30,4 +30,9 @@ impl FixedJoint {
             impulse: SpacialVector::zeros(),
         }
     }
+
+    /// Can a SIMD constraint be used for resolving this joint?
+    pub fn supports_simd_constraints(&self) -> bool {
+        true
+    }
 }