cc/gcc: add the backend/frontend infra for final gcc

Currently, we issue the bare-metal compiler from the pass_1 & pass_2
core compilers, because the final gcc breaks while doing so.

This implies we have to build some libces during the start_files step,
instead of the standard libc step. This is the case for newlib.

By adding a backend/frontend infra to the final gcc, we can abstract
what backend to call: the standard backend for non-bare-metal gcc,
and the core backend for bare-metal.

This patch is just an no-op, it just adds the final backend and
frontend without changing the way bare-metal is built, to come in a
subsequent patch.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

This is the README for crosstool-NG

Crosstool-NG follows the autoconf dance. So, to get you

kick-started, just run:

    ./configure --help

If you are using a development snapshot, you'll have to

create the configure script, first. Just run:

    ./bootstrap

You will find the documentation in the directory 'docs'.

Here is a quick overview of what you'll find there:

  0 - Table of content

  1 - Introduction

  2 - Installing crosstool-NG

  3 - Configuring a toolchain

  4 - Building the toolchain

  5 - Using the toolchain

  6 - Toolchain types

  7 - Contributing

  8 - Internals

  A - Credits

  B - Known issues

  C - Misc. tutorials

You can also point your browser at:

  http://crosstool-ng.org/

Aloha!