No unistd.h for macos 10

build.zig

const std = @import("std");
const CrossTarget = std.zig.CrossTarget;

pub fn build(b: *std.Build) void {
    const target = CrossTarget{
        .cpu_arch = .x86_64,
        .os_tag = .macos,
        .os_version_min = CrossTarget.OsVersion{ .semver = .{ .major = 10, .minor = 14, .patch = 0 } },
        .abi = .none,
    };
    const optimize = b.standardOptimizeOption(.{});

    var exe = b.addExecutable(.{
        .name = "test",
        .root_source_file = .{ .path = "test.zig" },
        .target = target,
        .optimize = optimize,
    });
    exe.linkLibC();
    exe.install();
}

test.zig

const std = @import("std");
const unistd = @cImport({@cInclude("unistd.h");});
pub fn main() !void {
    const ticks: i64 = unistd.sysconf(unistd._SC_CLK_TCK);
    std.debug.print("ticks = {}\n", .{ticks});
}