[lldb] Fix mod-while-iteration in IRForTarget (#203035)

We modify the IR module here while iterating over it. Use the usual list
trick to delay modification until after the loop.

This was uncovered by bccd1b9cb744e5dd96ee59baa4bf4583457feea3

GitOrigin-RevId: 6ee9d90c58c4c7194f3a552e01a3e44c376cdfbe