Don't consider a destination file modified until we've seen a #line
Don't consider a destination file modified until we've seen a #line

* If we have a merged file with #lines in it, then we want to split those #lines
  into separate files as expected. However the original merged file should be
  left alone. Previously this happened if the first thing we saw was a #line but
  that was only by coincidence. If there was some preamble before the first
  #line we'd start copying that and then stop once we started emitting lines
  into other files.

baldurk/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,baldurk/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,Zorro666/renderdoc,Zorro666/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,baldurk/renderdoc,Zorro666/renderdoc