Editing the code below from doomtype.h would be my first try at fixing it.
But, I am not sure which method I would use to fix it.

Tim S.

Code:
#ifndef __BYTEBOOL__
#define __BYTEBOOL__
// Fixed to use builtin bool type with C++.
#ifdef __cplusplus
typedef bool boolean;
#else
#ifdef __BEOS__	/* boolean is a builtin type for MWCC */
#define boolean D_BOOL
#undef false
#define false D_false
#undef true
#define true D_true
#endif
typedef enum {false, true} boolean;
#endif
typedef unsigned char byte;
#endif