re PR target/55974 ([avr] Wrong suffix for built-in defines __INT24_MAX__ and __UINT24_MAX__ with -mint8)

	PR target/55974
	* config/avr/avr-c.c (avr_cpu_cpp_builtins): Define __FLASH
	etc. to 1 and not to __flash.
	Use LL suffix for __INT24_MAX__ with -mint8.
	Use ULL suffix for __UINT24_MAX__ with -mint8.

From-SVN: r195169