Scalar -> vector not implicit in call or assign.

test/test_suite/vector/vector_conversion_scalar.c3

@@ -0,0 +1,14 @@
+fn void test2(int[<2>] x) {}
+fn void main()
+{
+  int[<2>] y = 1;
+  y[..] = 3;
+  y.xy = 3;       // #error: cannot use swizzling
+  y *= 2;
+  y = 3;          // #error: explicit cast
+  test2(3);       // #error: explicit cast
+  {|
+    if (y[0] == 3) return 1; // #error: explicit cast
+    return y;
+  |};
+}