Rollup merge of #143564 - Enselic:must_emit_unwind_tables-comment, r=oli-obk

compiler: Deduplicate `must_emit_unwind_tables()` comments

There is one comment at a call site and one comment in the function definition that are mostly saying the same thing. Fold the call site comment into the function definition comment to reduce duplication.

There are actually some inaccuracies in the comments but let's deduplicate before we address the inaccuracies.

Author: jieyouxu