The gccrs project is an ambitious
effort started in 2014 to implement a Rust compiler within The GNU Compiler
Collection (GCC). Even though the task is far from complete, progress has
been made since LWN’s previous coverage,
according to reports from the project. Meanwhile, another hybrid and more
mature approach to GCC Rust code generation is available in rustc_codegen_gcc.

Source: LWN.net – [$] Progress toward a GCC-based Rust compiler