Zig code fails due to recent change in zig

[JasonGross]

error: get this from @import("builtin") instead of std.builtin
pub const mode = @compileError("get this from @import(\"builtin\") instead of std.builtin");
                 ^
./src/curve25519_32.zig:16:25: note: referenced here
const mode = std.builtin.mode; // Checked arithmetic is disabled in non-debug modes to avoid side channels
                        ^
./src/curve25519_32.zig:826:23: note: referenced here
    @setRuntimeSafety(mode == .Debug);
                      ^
The following command exited with error code 1:

cc @jedisct1