Minor grammar fixes.
auto merge of #17420 : anchovieshat/rust/grammar, r=huonw

Fix grammar (double "note") in situations like:

src/reader/events.rs:120:5: 120:25 **note: note** conflicting type here
src/reader/events.rs:120     Error(common::Error)
Move -Z lto to -C lto.

Closes #12443
auto merge of #17421 : anchovieshat/rust/move_lto, r=thestinger

Closes #12443