You can specify forward declarations of enums, for example:

enum Incomplete_Enums_0;
int Incomplete_Enums_2 (enum Incomplete_Enums_0 * passon)
{
    return 0;
}
int Incomplete_Enums_1 (enum Incomplete_Enums_0 * passon)
{
    return Incomplete_Enums_2(passon);
}
enum Incomplete_Enums_0 { ALPHA, BETA, GAMMA };

Supported in GNU mode and ARM mode.