@alexcrichton I’m happy to report that on the latest nightly, rust-belt builds on Windows 10 successfully with ThinLTO without any explosions 
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nightly-x86_64-pc-windows-msvc updated - rustc 1.22.0-nightly (4750c1ec0 2017-10-19)
Normal
cargo +nightly build --release
Finished release [optimized] target(s) in 160.18 secs
ThinLTO
RUSTFLAGS='-C codegen-units=16 -Z thinlto'
cargo +nightly build --release
Finished release [optimized] target(s) in 154.72 secs
So that’s actually a speed-up of about 4% for this single data point.