Auto merge of #78399 - vn-ki:gsgdt-graphviz, r=oli-obk

make MIR graphviz generation use gsgdt

gsgdt [https://crates.io/crates/gsgdt] is a crate which provides an
interface for stringly typed graphs. It also provides generation of
graphviz dot format from said graph.

This is the first in a series of PRs on moving graphviz code out of rustc into normal crates and then implementating graph diffing on top of these crates.

r? `@oli-obk`

tests/ui/crashes/used_underscore_binding_macro.rs

@@ -1,7 +1,6 @@
-#![allow(clippy::useless_attribute)] //issue #2910
+// edition:2018
 
-#[macro_use]
-extern crate serde_derive;
+use serde::Deserialize;
 
 /// Tests that we do not lint for unused underscores in a `MacroAttribute`
 /// expansion