cpu_features_get_perf_counter seems incorrect for macOS

[barracuda156]

Looks like there is no case of macOS here:

libretro-common/features/features_cpu.c

Lines 155 to 214 in 668749a

	retro_perf_tick_t cpu_features_get_perf_counter(void)
	{
	retro_perf_tick_t time_ticks = 0;
	#if defined(_WIN32)
	long tv_sec, tv_usec;
	#if defined(_MSC_VER) && _MSC_VER <= 1200
	static const unsigned __int64 epoch = 11644473600000000;
	#else
	static const unsigned __int64 epoch = 11644473600000000ULL;
	#endif
	FILETIME file_time;
	SYSTEMTIME system_time;
	ULARGE_INTEGER ularge;
	GetSystemTime(&system_time);
	SystemTimeToFileTime(&system_time, &file_time);
	ularge.LowPart = file_time.dwLowDateTime;
	ularge.HighPart = file_time.dwHighDateTime;
	tv_sec = (long)((ularge.QuadPart - epoch) / 10000000L);
	tv_usec = (long)(system_time.wMilliseconds * 1000);
	time_ticks = (1000000 * tv_sec + tv_usec);
	#elif defined(GEKKO)
	time_ticks = gettime();
	#elif !defined(__MACH__) && !defined(__FreeBSD__) && (defined(_XBOX360) || defined(__powerpc__) || defined(__ppc__) || defined(__POWERPC__) || defined(__PSL1GHT__) || defined(__PPC64__) || defined(__powerpc64__))
	time_ticks = __mftb();
	#elif (defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK > 0) || defined(__QNX__) || defined(ANDROID)
	struct timespec tv;
	if (ra_clock_gettime(CLOCK_MONOTONIC, &tv) == 0)
	time_ticks = (retro_perf_tick_t)tv.tv_sec * 1000000000 +
	(retro_perf_tick_t)tv.tv_nsec;
	#elif defined(__GNUC__) && defined(__i386__) || defined(__i486__) || defined(__i686__) || defined(_M_X64) || defined(_M_AMD64)
	__asm__ volatile ("rdtsc" : "=A" (time_ticks));
	#elif defined(__GNUC__) && defined(__x86_64__) || defined(_M_IX86)
	unsigned a, d;
	__asm__ volatile ("rdtsc" : "=a" (a), "=d" (d));
	time_ticks = (retro_perf_tick_t)a | ((retro_perf_tick_t)d << 32);
	#elif defined(__ARM_ARCH_6__)
	__asm__ volatile( "mrc p15, 0, %0, c9, c13, 0" : "=r"(time_ticks) );
	#elif defined(__aarch64__)
	__asm__ volatile( "mrs %0, cntvct_el0" : "=r"(time_ticks) );
	#elif defined(PSP) || defined(VITA)
	time_ticks = sceKernelGetSystemTimeWide();
	#elif defined(ORBIS)
	sceRtcGetCurrentTick((SceRtcTick*)&time_ticks);
	#elif defined(PS2)
	time_ticks = ps2_clock();
	#elif defined(_3DS)
	time_ticks = svcGetSystemTick();
	#elif defined(WIIU)
	time_ticks = OSGetSystemTime();
	#elif defined(HAVE_LIBNX)
	time_ticks = armGetSystemTick();
	#elif defined(EMSCRIPTEN)
	time_ticks = emscripten_get_now() * 1000;
	#endif
	return time_ticks;
	}

x86 and arm64 will use arch-specific cases, but for powerpc there is nothing, since macOS is excluded here:

libretro-common/features/features_cpu.c

Lines 179 to 180 in 668749a

	#elif !defined(__MACH__) && !defined(__FreeBSD__) && (defined(_XBOX360) || defined(__powerpc__) || defined(__ppc__) || defined(__POWERPC__) || defined(__PSL1GHT__) || defined(__PPC64__) || defined(__powerpc64__))
	time_ticks = __mftb();