Update build-toolchain.sh for mac os

[alexvnesta]

This request will resolve
#461

It also addresses the isl issue - but only for mac os.
#460

My proposed changes:

1. Add additional homebrew dependencies for mac os

• they are specified in the libdragon compile from source guide, but it is more foolproof to add them in the configure script.

2. Require homebrew install of zlib on mac os.

• The system zlib throws a build error.

3. Remove the requirement for system zlib if on mac os.

• I made a platform check that uses system zlib if not on darwin, as I did not want to break other platforms.

I tested this by first removing all homebrew packages:

while [[ `brew list | wc -l` -ne 0 ]]; do
    for EACH in `brew list`; do
        brew uninstall --force --ignore-dependencies $EACH
    done
done

Then I cloned my modified repo and ran build-toolchain.sh on my m2 pro macbook running Mac OS Sonoma 14.2.1. Libdragon was able to successfully build without issue using these modifications.

Previously I would get errors not being able to find certain tools (like zlib, gcc, binutils, etc.). These errors are addressed by adding to the brew install -q command.

Please note, that I did not test other platforms. I am not sure if this will break regular mac os intel builds or non-mac os builds.

[alexvnesta]

@rasky I changed to if-else relying on the os-type as you suggested. Hopefully this looks better. Thanks for the suggestion!

[rasky]

Pushed also to stable.