add ./install_dependencies.sh script, update build commands

[henderkes]

maybe instead of #1565?

[henderkes]

I would also like to add information that the recommended way to build FrankenPHP is with xcaddy, given that users will expect mercure, vulcain and brotli to work.

[dunglas]

I'm not sure that's a good idea to include this script. End users should use the packages provided by their distributions for these dependencies, when available.

[dunglas]

It should be install-depdendencies.sh for consistency with other scripts.

Also, is bash really necessary? Alpine doesn't have Bash by default.

[henderkes]

Yes, bash is necessary for the way the script is written. I could rework it to work with posix shell, if you want, but I chose bash because build-static and build-packages also use bin/bash.

[henderkes]

I'm not sure that's a good idea to include this script. End users should use the packages provided by their distributions for these dependencies, when available.

I'm not sure if that's a good idea. Wtr-watcher doesn't exist as a package as far as I know and while brotli does exist, the brotli-devel static library is built without -fPIC, meaning it fails static linking and falls back to shared linking against libbrolienc, libbrotlidec and libbrolicommon.so. Users will end up with a frankenphp that links against shared libraries that they most likely won't have installed on their production system.

The worst part is that gcc falls back to linking against the shared libraries silently. A user will never know why it depends on libbrotli's shared libraries unless they use ldd and know about gcc's linking intricacies.