detectFromBuilding

pub fn detectFromBuilding(
    arena: Allocator,
    zig_lib_dir: []const u8,
    target: *const std.Target,
) !LibCDirs {
    const s = std.fs.path.sep_str;

    if (target.os.tag.isDarwin()) {
        const list = try arena.alloc([]const u8, 1);
        list[0] = try std.fmt.allocPrint(
            arena,
            "{s}" ++ s ++ "libc" ++ s ++ "include" ++ s ++ "any-macos-any",
            .{zig_lib_dir},
        );
        return .{
            .libc_include_dir_list = list,
            .libc_installation = null,
            .libc_framework_dir_list = &.{},
            .sysroot = null,
            .darwin_sdk_layout = .vendored,
        };
    }

    const generic_name = libCGenericName(target);
    // Some architecture families are handled by the same set of headers.
    const arch_name = if (target.isMuslLibC() or target.isWasiLibC())
        std.zig.target.muslArchNameHeaders(target.cpu.arch)
    else if (target.isGnuLibC())
        std.zig.target.glibcArchNameHeaders(target.cpu.arch)
    else if (target.isFreeBSDLibC())
        std.zig.target.freebsdArchNameHeaders(target.cpu.arch)
    else if (target.isNetBSDLibC())
        std.zig.target.netbsdArchNameHeaders(target.cpu.arch)
    else
        @tagName(target.cpu.arch);
    const os_name = @tagName(target.os.tag);
    const abi_name = if (target.isMuslLibC())
        std.zig.target.muslAbiNameHeaders(target.abi)
    else if (target.isGnuLibC())
        std.zig.target.glibcAbiNameHeaders(target.abi)
    else if (target.isNetBSDLibC())
        std.zig.target.netbsdAbiNameHeaders(target.abi)
    else
        @tagName(target.abi);
    const arch_include_dir = try std.fmt.allocPrint(
        arena,
        "{s}" ++ s ++ "libc" ++ s ++ "include" ++ s ++ "{s}-{s}-{s}",
        .{ zig_lib_dir, arch_name, os_name, abi_name },
    );
    const generic_include_dir = try std.fmt.allocPrint(
        arena,
        "{s}" ++ s ++ "libc" ++ s ++ "include" ++ s ++ "generic-{s}",
        .{ zig_lib_dir, generic_name },
    );
    const generic_arch_name = std.zig.target.osArchName(target);
    const arch_os_include_dir = try std.fmt.allocPrint(
        arena,
        "{s}" ++ s ++ "libc" ++ s ++ "include" ++ s ++ "{s}-{s}-any",
        .{ zig_lib_dir, generic_arch_name, os_name },
    );
    const generic_os_include_dir = try std.fmt.allocPrint(
        arena,
        "{s}" ++ s ++ "libc" ++ s ++ "include" ++ s ++ "any-{s}-any",
        .{ zig_lib_dir, os_name },
    );

    const list = try arena.alloc([]const u8, 4);
    list[0] = arch_include_dir;
    list[1] = generic_include_dir;
    list[2] = arch_os_include_dir;
    list[3] = generic_os_include_dir;

    return .{
        .libc_include_dir_list = list,
        .libc_installation = null,
        .libc_framework_dir_list = &.{},
        .sysroot = null,
        .darwin_sdk_layout = .vendored,
    };
}