produce configure-generated files using build options and target settings rather than hard-coding

[andrewrk]

The commit af01e2d copied configure-generated source files into the repo. These are incorrectly hard-coded with the settings of the host when ./configure was evaluated. Instead, all these files should be generated by build.zig at build time.

In addition to the commit listed above:

• libavutil/ffversion.h

[david-vanderson]

I am trying to fix this, but need guidance.

I tried (and failed) to get build.zig to create the .c files inside zig-cache and then add those to the C sources. Is there a way to do this? Or should build.zig create the files where they normally reside and reference the normal paths?

For the headers I was planning on replacing them with empty files in git, and putting all the #defines in build.zig. Sound right?

[andrewrk]

For the headers, you could try something like this:

https://github.com/andrewrk/libmp3lame/blob/497568e670bfeb14ab6ef47fb6459a2251358e43/build.zig#L8-L116

More enhancements to std.build will be needed to additionally install such a generated header.

As for .c files, all of these things need to be done in a declarative manner with the build system. Perhaps std.build.LibExeObjStep needs to gain a new method similar to addCSourceFile but that accepts a WriteFileStep as a parameter.

[david-vanderson]

First start on the headers part here ziglang/zig#14382

[david-vanderson]

Thanks for the guidance! That helped me understand where to start.