I'm working on a PR. The current version of build-installer.py doesn't use LTO/PGO because installers are build on macOS 10.9 where the compiler doesn't reliably support this. Recent compilers should work a lot better. The upcoming PR enables --enable-optimizations when building on macOS 10.15 or later (Xcode 11 or 12), mostly because that's what I'm testing with. I'm listing 41100 as a dependency because having that is the only way to make use of this PR at the moment: build-installer.py uses --enable-universalsdk and 41100 introduces "universal2" as a set of architectures that can be build using Xcode 12. All other sets of architectures require Xcode 10 or older.
Thanks for the PR. I am only going to apply this to the 3.10 branch for now. Perhaps when we have more experience with it, it could be backported to 3.9.x. First appearance in 3.10.0b1.