Oh, sorry for the confusion: this is about rustc_codegen_gcc which is a codegen plugin for rustc that uses libgccjit to generate the object files via GCC instead of LLVM, so it still requires rustc. There's another project that is a GCC frontend, called gccrs. Also, bootstrap is overloaded: in this case, a full bootstrap means that we can compile the Rust compiler with rustc_codegen_gcc, producing a stage-2 compiler, then recompile the Rust compiler with this stage-2 compiler to get a stage-3 compiler and those 2 compares as equal.