DOCS: INTERPROCEDURAL_OPTIMIZATION only covers old behavior
The docs for INTERPROCEDURAL_OPTIMIZATION only cover the pre-3.9 behavior, where it's fine to set this to "ON" even if your compiler does not support ipo. They should mention the new behavior and link to CheckIPOSupported, similar to what's done here: https://cliutils.gitlab.io/modern-cmake/chapters/features/small.html#interprocedural-optimization .