std: Optimize functions that deal with bool vectors for x86.

[notcancername]

Add doc comments. Add tests.

[notcancername]

No benchmark, but: https://godbolt.org/z/7nqP6zqYr

[notcancername]

This seems to cause some issues with the C backend? Should I add a workaround for that? Or skip the tests for CBE?

[andrewrk]

Your godbolt link shows x86_64 but your logic tests for both x86 and x86_64:

zig/lib/std/target.zig

Lines 874 to 879 in 7ab306d

	pub inline fn isX86(arch: Arch) bool {
	return switch (arch) {
	.x86, .x86_64 => true,
	else => false,
	};
	}

Is the new code better for 32-bit x86 as well?

[andrewrk]

I asked this question in the previous review:

Your godbolt link shows x86_64 but your logic tests for both x86 and x86_64:
Is the new code better for 32-bit x86 as well?

I don't see an answer to this question.

[notcancername]

The answer is yes.

[andrewrk]

CI checks failing, no updates in 30+ days.