riscv-gnu-toolchain commit referenced is outdated

[benreynwar]

The riscv-gnu-toolchain repo commit that is checked out when running piton/ariane_build_tools.sh (which in turn calls piton/design/chip/tile/ariane/ci/build-riscv-gcc.sh) is from 2017. Some git submodules don't even exist anymore.

I assume that no-one actually uses this script to build these dependencies, and already have the $RISCV variable pointing at a working installation. It probably worth making this the default approach in the installation instructions.

[Jbalkind]

Thanks Ben. Yeah once we get ariane bumped (Joan has a draft PR) there should be new scripts which build gcc 13. Personally I'd rather people used prepackaged cross compilers