Use just-built curl to generate zsh completion

[ismail]

In a Linux build environment curl is built in a chroot where there is no curl installed on the system. In that case currently curl fails to build zsh completion. Producing a broken _curl file. Instead we can use the just-built curl binary to generate zsh completion. This way completion will also be always up-to-date with new options too.

[mention-bot]

By analyzing the blame information on this pull request, we identified @ghedo and @danielshahaf to be potential reviewers

[dfandrich]

While I'm for this idea in the native build case, it will fail in the cross-compiled case. Also, I'm not sure a relative path is going to work in an out-of-tree build; it's probably better to pass in the path to the curl binary on the command-line.

[ismail]

I tested the out-of-tree builds and it works fine. Cross compilation is not supported as you noted but that doesn't make sense either. System curl != curl you build.

[danielshahaf]

@ismail I think @dfandrich's is saying that your patch breaks cross-builds that pass --with-zsh-functions-dir, since they will attempt to execute ../src/curl [which will likely fail]. In other words: I think @dfandrich is asking you to change the patch such that cross-builds don't attempt to run ../src/curl.

However, I'm not sure what cross-builds should do. The up-to-date options list is embedded in a C file, but the cross-build can't assume a native compiler is installed [to compile a small, native program that only implements curl -h and nothing else], can it?

[bagder]

Also, a duplicate of #582 it seems

[ghedo]

This is also the wrong way to fix this. The default "curl" is meant to use the system-provided curl for testing purposes, and this breaks that.

[ismail]

@bagder Indeed, I'll close this one. Thanks!