check if bprintf is defined before declaring prototype (does this solve your issue twinaphex?)

src/burn/burn.cpp

@@ -8,7 +8,9 @@
 // filler function, used if the application is not printing debug messages
 static INT32 __cdecl BurnbprintfFiller(INT32, TCHAR* , ...) { return 0; }
 // pointer to burner printing function
+#ifndef bprintf
 INT32 (__cdecl *bprintf)(INT32 nStatus, TCHAR* szFormat, ...) = BurnbprintfFiller;
+#endif
 
 INT32 nBurnVer = BURN_VERSION;		// Version number of the library
 

src/burn/burn.h

@@ -209,7 +209,9 @@ extern UINT32 *pBurnDrvPalette;
 #define PRINT_IMPORTANT (2)
 #define PRINT_ERROR		(3)
 
+#ifndef bprintf
 extern INT32 (__cdecl *bprintf) (INT32 nStatus, TCHAR* szFormat, ...);
+#endif
 
 INT32 BurnLibInit();
 INT32 BurnLibExit();