Fix name collision between C enum and typedef (#2326)

Fixes #2008.

Example:

```c
enum Enum { Variant };
typedef int16_t Enum;
```

This is valid and idiomatic C (though not valid C++). `cbindgen` uses this idiom as the default C translation of Rust enums, the equivalent of what would be `enum Enum : int16_t { Variant };` in C++.

`bindgen header.h` before:

```rust
pub const Enum_Variant: Enum = 0;
pub type Enum = ::std::os::raw::c_uint;
pub type Enum = i16;
```

```console
error[E0428]: the name `Enum` is defined multiple times
 --> generated.rs:3:1
  |
2 | pub type Enum = ::std::os::raw::c_uint;
  | --------------------------------------- previous definition of the type `Enum` here
3 | pub type Enum = i16;
  | ^^^^^^^^^^^^^^^^^^^^ `Enum` redefined here
  |
  = note: `Enum` must be defined only once in the type namespace of this module
```

After:

```rust

pub const Enum_Variant: Enum = 0;
pub type Enum = i16;
```

0 files changed, 0 insertions, 0 deletions