backport Rohit's vectorized quaternion product

Eigen/src/Core/arch/SSE/PacketMath.h

@@ -315,4 +315,7 @@ struct ei_palign_impl<Offset,__m128d>
 };
 #endif
 
+#define ei_vec4f_swizzle1(v,p,q,r,s) \
+  (_mm_castsi128_ps(_mm_shuffle_epi32( _mm_castps_si128(v), ((s)<<6|(r)<<4|(q)<<2|(p)))))
+
 #endif // EIGEN_PACKET_MATH_SSE_H

Eigen/src/Core/util/Constants.h

@@ -239,4 +239,16 @@ enum {
   HasDirectAccess = DirectAccessBit
 };
 
+const int EiArch_Generic = 0x0;
+const int EiArch_SSE     = 0x1;
+const int EiArch_AltiVec = 0x2;
+
+#if defined EIGEN_VECTORIZE_SSE
+  const int EiArch = EiArch_SSE;
+#elif defined EIGEN_VECTORIZE_ALTIVEC
+  const int EiArch = EiArch_AltiVec;
+#else
+  const int EiArch = EiArch_Generic;
+#endif
+
 #endif // EIGEN_CONSTANTS_H