Remove vector casts for c++ compilation.

src/dimension.h

@@ -275,11 +275,15 @@ __attribute__((always_inline)) INLINE static vector pow_dimension_vec(
 
 #if defined(HYDRO_DIMENSION_3D)
 
-  return (vector)(vec_mul(vec_mul(x.v, x.v), x.v));
+  vector x3;
+  x3.v = vec_mul(vec_mul(x.v, x.v), x.v);
+  return x3;
 
 #elif defined(HYDRO_DIMENSION_2D)
 
-  return (vector)(vec_mul(x.v, x.v));
+  vector x2;
+  x2.v = vec_mul(x.v, x.v);
+  return x2;
 
 #elif defined(HYDRO_DIMENSION_1D)
 
@@ -304,16 +308,22 @@ __attribute__((always_inline)) INLINE static vector pow_dimension_plus_one_vec(
 
 #if defined(HYDRO_DIMENSION_3D)
 
-  const vector x2 = (vector)(vec_mul(x.v, x.v));
-  return (vector)(vec_mul(x2.v, x2.v));
+  vector x2, x4;
+  x2.v = vec_mul(x.v, x.v);
+  x4.v = vec_mul(x2.v, x2.v);
+  return x4;
 
 #elif defined(HYDRO_DIMENSION_2D)
 
-  return (vector)(vec_mul(x.v, vec_mul(x.v, x.v)));
+  vector x3;
+  x3.v = vec_mul(vec_mul(x.v, x.v), x.v);
+  return x3;
 
 #elif defined(HYDRO_DIMENSION_1D)
-
-  return (vector)(vec_mul(x.v, x.v));
+  
+  vector x2;
+  x2.v = vec_mul(x.v, x.v);
+  return x2;
 
 #else