Followup GH-4993: drop vector-cast for casting fat values

Author: kubo39

gen/llvmhelpers.cpp

@@ -675,7 +675,7 @@ DValue *DtoCastStruct(Loc loc, DValue *val, Type *to) {
 
   // A cast between fat values is possible only when the sizes match.
   // https://github.com/ldc-developers/ldc/issues/4993
-  if (totype->ty == TY::Tsarray || totype->ty == TY::Tvector) {
+  if (totype->ty == TY::Tsarray) {
     if (size(totype) == size(val->type->toBasetype())) {
       llvm::Value *lval = DtoLVal(val);
       return new DLValue(to, lval);

tests/compilable/gh4993.d

@@ -2,15 +2,7 @@
 
 struct Foo {}
 
-struct Bar
-{
-    int[4] v;
-}
-
 void main() {
     Foo f;
     auto x = cast(ubyte[Foo.sizeof])f;
-
-    Bar b;
-    auto y = cast(__vector(int[4]))b;
 }