Added initial NEON support, most tests pass however we had to use some hackish workarounds

as gcc on ARM (both CodeSourcery 4.4.1 used and experimental 4.5) fail to
ensure proper alignment with __attribute__((aligned(16))). This has to be
fixed upstream to remove the workarounds.

Eigen/Core

@@ -111,6 +111,10 @@
     #undef bool
     #undef vector
     #undef pixel
+  #elif defined  __ARM_NEON__
+    #define EIGEN_VECTORIZE
+    #define EIGEN_VECTORIZE_NEON
+    #include "arm_neon.h"
   #endif
 #endif
 
@@ -165,6 +169,8 @@ inline static const char *SimdInstructionSetsInUse(void) {
   return "SSE, SSE2";
 #elif defined(EIGEN_VECTORIZE_ALTIVEC)
   return "AltiVec";
+#elif defined(EIGEN_VECTORIZE_NEON)
+  return "ARM NEON";
 #else
   return "None";
 #endif
@@ -204,6 +210,8 @@ struct Dense {};
   #include "src/Core/arch/SSE/MathFunctions.h"
 #elif defined EIGEN_VECTORIZE_ALTIVEC
   #include "src/Core/arch/AltiVec/PacketMath.h"
+#elif defined EIGEN_VECTORIZE_NEON
+  #include "src/Core/arch/NEON/PacketMath.h"
 #endif
 
 #ifndef EIGEN_CACHEFRIENDLY_PRODUCT_THRESHOLD