Zsh: add build-time dependency on autoconf and add CFLAGS for more recent LLVM

[taliaferro]

This PR fixes two issues with zsh.

1. It seems zsh has a build-time dependency on autoconf. (It looks like it's re-running it later in the process and not finding it when it needs it)

2. Add two compiler flags (-Wno-implicit-int and -Wno-implicit-function-declaration) when building with newer versions of LLVM.

Without the latter, the build would complete successfully, but the resulting zsh would lock up and become unresponsive to signals the first time it encounters process substitution. (this issue can be demonstrated by running timeout 3 zsh -c '$(echo echo success)' || echo failure.)

[taliaferro]

@spackbot fix style, if you'd be so kind

[spackbot-app]

Let me see if I can fix that for you!

[spackbot-app]

I was able to run spack style --fix for you!

spack style --fix

repos/spack_repo/builtin/packages/zsh/package.py
�[1;34m==> �[0mrunning ruff format
1 file reformatted
�[1;34m==> �[0mrunning ruff check
All checks passed!
�[1;34m==> �[0mstyle checks passed

Keep in mind that I cannot fix your flake8 or mypy errors, so if you have any you'll need to fix them and update the pull request. If I was able to push to your branch, if you make further changes you will need to pull from your updated branch before pushing again.

I've updated the branch with style fixes.

[alalazo]

I think there's an issue with operator precedence here:

>>> False and False or True
True

(%apple-clang is always True regardless of name)