hook up result locations for union initializations

```zig
export fn entry() void {
    var x = Foo{ .bar = bar() };
}
```

```llvm
define void @entry() #2 !dbg !44 {
Entry:
  %x = alloca %Foo, align 4
  %0 = getelementptr inbounds %Foo, %Foo* %x, i32 0, i32 1, !dbg !68
  store i1 true, i1* %0, align 1, !dbg !68
  %1 = getelementptr inbounds %Foo, %Foo* %x, i32 0, i32 0, !dbg !68
  %2 = bitcast { i32, [4 x i8] }* %1 to %Bar*, !dbg !68
  call fastcc void @bar(%Bar* sret %2), !dbg !68
  call void @llvm.dbg.declare(metadata %Foo* %x, metadata !48, metadata !DIExpression()), !dbg !69
  ret void, !dbg !70
}
```
1a51bf6304Andrew Kelley committed on 6/10/2019, 3:15:32 PMparent4e2b282
5 files changedLine totals unavailable