Fix Thin LTO not working

[TCROC]

This PR fixes this issue: #21947. I have tested compiling the Godot Game Engine with this PR: https://github.com/godotengine/godot

It compiles much faster and does not consume all of my memory! :)

This is vital for us to be able to add first class support for cross platform compilation in our godot-src project: https://github.com/lange-studios/godot-src

NOTE:

I am unsure of how to trigger the code path in main.zig in lines 1383 - 1396. If someone could give me instructions on how to trigger that code path or test themselves to confirm that code change works, that would be greatly appreciated!

Thanks again for the awesome Zig! U all rock! :)

[alexrp]

I am unsure of how to trigger the code path in main.zig in lines 1383 - 1396. If someone could give me instructions on how to trigger that code path or test themselves to confirm that code change works, that would be greatly appreciated!

That would be for zig build-exe, build-lib, test, etc... the other code path is for zig cc and zig c++.

[TCROC]

@alexrp looks like one of the pipelines failed. Doesn't jump out to me as something introduced by this PR. Likely just needs a rerun. Let me know if you think otherwise

[alexrp]

In this path, we're supposed to resolve a default value if the user has not provided one. We already checked options.lto != .none above, so this can only possibly resolve to .none.

This should probably be:

Suggested change

	.ReleaseSafe, .ReleaseFast, .ReleaseSmall => options.lto,
	.ReleaseSafe, .ReleaseFast, .ReleaseSmall => .full,

We can consider later if the default should be switched to .thin. I don't know if there are any major disadvantages to it that would make .full a preferable default.

[alexrp]

@TCROC ping; I think this hunk is the only blocker for merging this.

[alexrp]

It would also be nice to change std.Build to support enum { none, full, thin }. That's not a requirement to merge this, though.

[TCROC]

It would also be nice to change std.Build to support enum { none, full, thin }. That's not a requirement to merge this, though.

Sounds like a plan! I look forward to testing your PR after this one goes through! :)