Duplicate members in C runtime with imports: duplicate member 'g'

## Steps to reproduce

```
// Option.g
grammar Option;

options {
language=C;
}

import Option2, Option3;

source
: source_item+
;

```

```
// Option2.g
parser grammar Option2;

source_item
: test
;
```

```
// Option3.g

parser grammar Option3;

test
: 'a'
;
```

Generate C code:

```
java -jar antlr-complete-3.5.3.jar Option.g
```

In `OptionParser.h` struct elements have duplicated names:

```c
// OptionParser.h

struct OptionParser_Ctx_struct
{
pANTLR3_PARSER pParser;
pOption_Option2 g;
pOption_Option3 g;

...
};
```

## Expected behavior

No duplicated names.

Like when using Java runtime:

```Java
@SuppressWarnings("all")
public class OptionParser extends Parser {
// delegates
public Option_Option2 gOption2;
public Option_Option3 gOption3;
public Parser[] getDelegates() {
return new Parser[] {gOption2, gOption3};
}
...
}
```

## Versions
```
Java: openjdk 17.0.12 2024-07-16
ANTLR3: 3.5.3
```

Reproduce the generation using Option.g, Option2.g, and Option3.g with the shown Java command, then inspect the generated OptionParser.h. Compare the C delegate members with the Java output and verify that the generated C struct contains distinct names for the imported grammars.

Written by the indexing model from the issue text.