handle OptionsStep in build_runner

[leecannon]

This allows generated files from OptionsStep to be resolved.

This is dependant on ziglang/zig#13003 I will leave it as a draft until it is merged.

I'm not 100% happy with this due to:

• We can't know how costly the dependencies of the step might be so i've decided to only support OptionsSteps that have no dependencies.
  Thankfully this is the most common situation, I don't think i've ever seen an OptionsStep have any dependencies.
• It's extremely common for the pacakge to be called build_options, this could easily result in multiple packages with the same name pointing to different files.
  As before this is an uncommon issue to hit as multiple OptionsSteps is rare.
  This is one more reason the TODO in build_runner.zig would be nice to fix.
  

  zls/src/special/build_runner.zig

  Lines 93 to 95 in 8cf93fc

  	// TODO: We currently add packages from every LibExeObj step that the install step depends on.
  	// Should we error out or keep one step or something similar?
  	// We also flatten them, we should probably keep the nested structure.

Before:

$ /home/lee/bin/zig run /home/lee/src/zls/src/special/build_runner.zig --cache-dir /home/lee/.cache/zls --pkg-begin @build@ build.zig --pkg-end -- /home/lee/bin/zig /home/lee/src/fff/ zig-cache ZLS_DONT_CARE
{
    "packages": [
        {
            "name": "args",
            "path": "libraries/zig-args/args.zig"
        },
        {
            "name": "known_folders",
            "path": "libraries/known-folders/known-folders.zig"
        },
        {
            "name": "bestline",
            "path": "libraries/bestline/bestline.zig"
        },
        {
            "name": "tracy",
            "path": "libraries/tracy/tracy.zig"
        },
        {
            "name": "zriscv",
            "path": "zriscv/zriscv.zig"
        },
        {
            "name": "bitjuggle",
            "path": "libraries/zig-bitjuggle/bitjuggle.zig"
        }
    ],
    "include_dirs": [
        "libraries/bestline/bestline"
    ]
}%

After:

$ /home/lee/bin/zig run /home/lee/src/zls/src/special/build_runner.zig --cache-dir /home/lee/.cache/zls --pkg-begin @build@ build.zig --pkg-end -- /home/lee/bin/zig /home/lee/src/fff/ zig-cache ZLS_DONT_CARE
{
    "packages": [
        {
            "name": "build_options",
            "path": "/home/lee/src/zriscv/zig-cache/options/_OHWmub1P7ZxHbsba8NlAXpkS2ryAiTxuWgRR8iH9_AHeEPbLP9T8iSLLH4QQeqm"
        },
        {
            "name": "args",
            "path": "libraries/zig-args/args.zig"
        },
        {
            "name": "known_folders",
            "path": "libraries/known-folders/known-folders.zig"
        },
        {
            "name": "bestline",
            "path": "libraries/bestline/bestline.zig"
        },
        {
            "name": "tracy",
            "path": "libraries/tracy/tracy.zig"
        },
        {
            "name": "zriscv",
            "path": "zriscv/zriscv.zig"
        },
        {
            "name": "bitjuggle",
            "path": "libraries/zig-bitjuggle/bitjuggle.zig"
        }
    ],
    "include_dirs": [
        "libraries/bestline/bestline"
    ]
}%

[leecannon]

ziglang/zig#13003 has been merged, might be best to wait for ziglang download to update before merging this though.

[SuperAuguste]

This is awesome! :)

This combined with #688 and #683 means we're really stepping up our build.zig completions :P

Btw, about your concerns; I personally believe in Andreas Kling(?)'s mindset that features shouldn't have to be 100% complete or perfect and that many people building them one block at a time is a lot more effective, so either you or someone else will come along and (hopefully :P) address these TODOs.

LGTM!