Fix recursion discovery in ipa-pure-const

Fix recursion discovery in ipa-pure-const

We make self recursive functions as looping of fear of endless recursion.
This is done correctly for local pure/const and for non-trivial SCCs in
callgraph, but for trivial SCCs we miss the flag.

I think it is bad decision since infinite recursion will run out of stack,
but changing it upsets some testcases and should be done independently.
So this patch is fixing current behaviour to be consistent.

gcc/ChangeLog:

2021-11-11  Jan Hubicka  <hubicka@ucw.cz>

	* ipa-pure-const.c (propagate_pure_const): Self recursion is
	a side effects.