This patchlet represents the impact of insn ashrqi3 on CC by means of attribute
"cc" instead of hard-coding it in notice_update_cc.

Testsuite passes fine. Moreover, tested against code like

char c;

void func_1 (char a)
{
    a = a >> 7;
    if (a)
        c = a;
}

that triggered PR39633.

Ok?

Johann

	* config/avr/avr.md (ashrqi3): Split alternative "n"
	into its remaining parts C03, C04, C05, C06, C07 and describe
	impact on CC by attribute "cc" appropriately.
	* config/avr/avr.c (notice_update_cc): Clean-up: Don't patch CC0
	by digging RTX.