Let me explain this patch. Ubuntu has changed its default to enable LTO (link-time global optimization) in building packages, and reported a bug in mit-scheme on the Debian bug tracker. That's how this issue came to my attention. In addition to tracking it down and fixing it (pretty trivial, although someone should double check that the signatures I ended up using are correct) I did some benchmarking to check if it would make sense to override the distribution's default and forcibly enable or disable LTO.
Bottom line: on amd64, LTO gives ~10% speedup to the interpreter, and ~2.5% speedup to compiled (native or SVM) Scheme code. Details: https://salsa.debian.org/debian/mit-scheme/-/blob/debian/debian/BENCHMARKS.md
