Disable link-time optimization (LTO) in release mode
Disable link-time optimization (LTO) in release mode

See https://gitlab.gnome.org/GNOME/librsvg/issues/523 for the
timings.

Initially I added LTO during the very early stages of Rustification,
because it didn't seem to affect things very much.  Now that
everything is in Rust, it *does* affect things very much :)

I suppose downstreams can make the decision to use LTO or not
themselves.

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