Where in the GCC source code does it compile to the different assembly languages?

Where is the code in the GCC source code that actually constructs the assembly for the different architectures?

Wondering how many different assembly languages it compiles to, and how it actually does this (by taking a look at the source code).

Is it in the gcc repo somewhere, or in another repo? I have started to dig around but haven't found anything.

https://github.com/gcc-mirror/gcc

For example, here is some of the assembly generating code in V8:

https://github.com/v8/v8-git-mirror/tree/master/src/x64

Is there anything equivalent for GCC?

I am wondering because it's a mystery how GCC does this, and it would be a great way to learn how compilers are actually implemented down to the assembly level.