hook up while on error unions with result locations
```zig
export fn entry() void {
var c: anyerror!i32 = 1234;
var x = while (c) |y| break foo() else |e| bar();
}
```
```llvm
define void @entry() #2 !dbg !39 {
Entry:
%c = alloca { i16, i32 }, align 4
%x = alloca %Foo, align 4
%0 = bitcast { i16, i32 }* %c to i8*, !dbg !56
call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %0, i8* align 4 bitcast ({ i16, i32 }* @0 to i8*), i64 8, i1 false), !dbg !56
call void @llvm.dbg.declare(metadata { i16, i32 }* %c, metadata !43, metadata !DIExpression()), !dbg !56
br label %WhileCond, !dbg !57
WhileCond: ; preds = %Entry
%1 = getelementptr inbounds { i16, i32 }, { i16, i32 }* %c, i32 0, i32 0, !dbg !58
%2 = load i16, i16* %1, align 2, !dbg !58
%3 = icmp ne i16 %2, 0, !dbg !58
br i1 %3, label %WhileElse, label %WhileBody, !dbg !58
WhileBody: ; preds = %WhileCond
%4 = getelementptr inbounds { i16, i32 }, { i16, i32 }* %c, i32 0, i32 1, !dbg !57
call void @llvm.dbg.declare(metadata i32* %4, metadata !50, metadata !DIExpression()), !dbg !57
call fastcc void @foo(%Foo* sret %x), !dbg !59
br label %WhileEnd, !dbg !60
WhileElse: ; preds = %WhileCond
%5 = getelementptr inbounds { i16, i32 }, { i16, i32 }* %c, i32 0, i32 0, !dbg !61
call void @llvm.dbg.declare(metadata i16* %5, metadata !51, metadata !DIExpression()), !dbg !61
call fastcc void @bar(%Foo* sret %x), !dbg !61
br label %WhileEnd, !dbg !57
WhileEnd: ; preds = %WhileElse, %WhileBody
call void @llvm.dbg.declare(metadata %Foo* %x, metadata !52, metadata !DIExpression()), !dbg !62
ret void, !dbg !63
}
```