Increase C++ performance in Lesson 265

[KlasterK]

LTO

In Rust, LTO is enabled:

lto = "fat"            # Enables full link-time optimization for better inlining and dead code elimination across crates.

While in C++ it isn't. Add this flag in CMakeLists:

set(CMAKE_INTERPROCEDURAL_OPTIMIZATION ON)

TUs count

In Rust version, there's only one TU, main.rs. While in C++ we have 5 files, and without LTO, inlines are not possible. LTO will fix TUs count problem, but maybe it will be even better to keep the code in 1 TU like in Rust version.

Compilers

C++ version may use different compilers depending on platform and toolchain. rustc is based on LLVM, so C++ should be compiled with a compiler based on LLVM too, which is clang++. Add an LLVM toolchain so compilers won't differ across platforms.

P.S. I didn't watch the video, a fellow of mine shared the comparison of C++ and Rust results and I started digging and noticed these omissions.