frotz compilation fails with gcc-15 due to C23 defining `bool`

[NHOrus]

C99 defined bool macro optionally in stdbool.h. C23 made bool reserved keyword.

Use stdbool.h instead of

spectrum2/backends/frotz/dfrotz/common/frotz.h

Lines 14 to 24 in b1770fc

	#ifndef __UNIX_PORT_FILE
	#include <signal.h>
	typedef int bool;
	#ifndef TRUE
	#define TRUE 1
	#endif
	#ifndef FALSE
	#define FALSE 0
	#endif

upstream fortz fixes it in https://gitlab.com/DavidGriffith/frotz/-/commit/dc6b7a7413a753e4b1583094a94a17590d393152

see also: gentoo bug https://bugs.gentoo.org/969771
see https://wiki.gentoo.org/wiki/Modern_C_porting#bool for causes