`derive(IntoBytes)` fails on `repr(C)` DSTs with parameterized leading fields

[jswrenn]

For example, compiling:

use zerocopy::IntoBytes;

#[derive(IntoBytes)]
#[repr(C)]
struct Struct {
    leading: Unalign<u32>,
    trailing: [u8]
}

...fails with this error:

error: no rules expected `<`
   --> src/lib.rs:6:18
    |
  6 |     addr: Unalign<u32>,
    |                  ^ no rules expected this token in macro call
    |
note: while trying to match `]`
   --> /playground/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/zerocopy-0.8.27/src/util/macro_util.rs:388:25
    |
388 |     ($t:ty, [$($ts:tt),*]) => {{

The failure arises because our internal repr_c_struct_has_padding macro accepts field types as comma delimited tts, but Unalign<u32> is not a single tt.

We should see if there's a minor patchup we can do to make this work. Unalign<u32> can be made to parse as a tt by parenthesizing it.

[joshlf]

The fix in #2836 is now published in 0.8.31.