Thanks, I'll add MSVC in my next round of updates! :)
MSVC's LTCG (LTO) pipeline has been heavily in use at Microsoft for decades now. PGO and LTCG go together. LTCG is the default way most of our binaries are built.
A lot of work has been done to make MSVC LTCG fast and scalable. In particular, the compiler backend is multithreaded on a per-function basis, and there is also support for incremental LTCG that reuses previously compiled machine code and summary information.