copy elision: implicit cast optional wrap when payload is integer

```zig
export fn entry() void {
    var a: i32 = 1234;
    var b: ?i32 = a;
}
```

```llvm
define void @entry() #2 !dbg !41 {
Entry:
  %a = alloca i32, align 4
  %b = alloca { i32, i1 }, align 4
  store i32 1234, i32* %a, align 4, !dbg !55
  call void @llvm.dbg.declare(metadata i32* %a, metadata !45, metadata !DIExpression()), !dbg !55
  %0 = load i32, i32* %a, align 4, !dbg !56
  %1 = getelementptr inbounds { i32, i1 }, { i32, i1 }* %b, i32 0, i32 1, !dbg !57
  store i1 true, i1* %1, align 1, !dbg !57
  %2 = getelementptr inbounds { i32, i1 }, { i32, i1 }* %b, i32 0, i32 0, !dbg !57
  store i32 %0, i32* %2, align 4, !dbg !57
  call void @llvm.dbg.declare(metadata { i32, i1 }* %b, metadata !48, metadata !DIExpression()), !dbg !57
  ret void, !dbg !58
}
```

Author: andrewrk

src/all_types.hpp

@@ -2338,7 +2338,6 @@ struct IrInstructionLoadPtr {
     IrInstruction base;
 
     IrInstruction *ptr;
-    IrInstruction *result_loc;
 };
 
 struct IrInstructionStorePtr {