[clang] Make -frewrite-includes put an endif at the end of the included text (PR #67613)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This looks great/useful to me.  I have no problems with it, but would like to give this a bit of time for others to review.  If this doesn't get other comments by friday next week, I'll approve.

https://github.com/llvm/llvm-project/pull/67613