Rollup merge of rust-lang#122334 - GuillaumeGomez:vendor-cg_gcc, r=Mark-Simulacrum

Vendor rustc_codegen_gcc

I used rust-lang#115274 as base for this update.

r? `@bjorn3`

Author: GuillaumeGomez

Cargo.lock

@@ -22,7 +22,7 @@ master = ["gccjit/master"]
 default = ["master"]
 
 [dependencies]
-gccjit = { git = "https://github.com/antoyo/gccjit.rs" }
+gccjit = "2.0"
 
 # Local copy.
 #gccjit = { path = "../gccjit.rs" }