GNU autoconf based build script and Github Actions CI

[NoMore201]

This PR introduces the following changes:

GNU autoconf based build script

Custom bash script are replaced by a new build system based on GNU autoconf. It is heavily inspired by RiscV toolchain build system. The idea is simple, to have a single configure script to handle building an installing compiler into a prefix folder. This configure script is automatically generated by autoconf by reading the configure.ac template.

With this new approach, a common cross-compiler build would look like this:

mkdir build && cd build
../configure --prefix /opt/gcc/linux
make -j$(nproc)

Github Actions pipeline

Added Github Actions configuration that run a pipeline on each push and pull-request onto main branch. Each pipeline run will also produce compiler artifact, consisting on linux and windows build of the compiler. You can see an example of a successfully run pipeline here in my fork: https://github.com/NoMore201/tricore-gcc-toolchain/actions/runs/11463697465

Automated release artifacts from Actions

When a new release is created through the Release functionality of Github, compiler build packages for both linux and windows are automatically downloaded from CI pipeline that run on the same commit as the release tag. You can see an example of a release in my fork: https://github.com/NoMore201/tricore-gcc-toolchain/releases

I think it would be really useful to have official releases of the compiler now that it seems to gather some interest.