[Clang] Add Clang Driver option to control Microsoft anonymous struct/union extensions

Add a new Clang Driver option `-fms-anonymous-structs` to enable Microsoft anonymous struct/union support independently from `-fms-extensions`.

This is needed to support code that uses anonymous structs extensively while avoiding conflicts with other Microsoft extensions (particularly `__ptr32`/`__ptr64` keywords).

The following program demonstrates this issue:

```c
#include
struct wInode
{
int x;
};
struct inode {
struct wInode;
};
int main()
{
struct inode p;
p.x = 20;
printf ("%d\n",p.x);
return 0;
}
```

```console
# clang -m64 -pthread -o out unnamed_struct.c -fms-extensions
In file included from unnamed_struct.c:1:
In file included from /usr/include/stdio.h:482:
/usr/include/sys/types.h:260:9: error: '__ptr32' attribute only applies to pointer arguments
260 | typedef __ptr32 mid_t; /* module ID */
| ^
/usr/include/sys/types.h:551:23: error: expected identifier or '('
551 | typedef void * __ptr64;
| ^
unnamed_struct.c:9:2: warning: anonymous structs are a Microsoft extension [-Wmicrosoft-anon-tag]
9 | struct wInode;
| ^
1 warning and 2 errors generated.
```

**Desired Behavior**:
Enable only the anonymous struct and union feature from Microsoft extensions.