I am trying to compile a new rust toolchain from source.
Something like the following
```
./x setup dist
./x build --target "x86_74-unknown-linux-gnu,aarch64-unknown-linux-gnu"
```

The build fails when building stage2 library artifacts for aarch64.
It looks like it is trying to link with `gcc` command, which is obviously not going to work.
Why is it using gcc instead of the llvm toolchain it has spent so much time building?
Am I doing something wrong, or is it really supposed to require a gcc toolchain for each stage2 library artifact to build?