ipa: Release body of clone_of when removing its last clone (PR 100413)

In the PR, the verifier complains that we did not manage to remove the
body of a node and it is right.  The node is kept for materialization
of two clones but after one is materialized, the other one is removed
as unneeded (as a part of delete_unreachable_blocks_update_callgraph).
The problem is that the node removal does not check for this situation
and can leave the clone_of node there with a body attached to it even
though there is no use for it any more.  This patch does checks for it
and handles the situation in a simlar way that
cgraph_node::materialize_clone does it, except that it also has to be
careful that the removed node itself does not have any clones, which
would still need the clone_of's body.  Failing to do that results in a
bootstrap failure.

gcc/ChangeLog:

2022-04-27  Martin Jambor  <mjambor@suse.cz>

	PR ipa/100413
	* cgraph.cc (cgraph_node::remove): Release body of the node this
	is clone_of if appropriate.

gcc/testsuite/ChangeLog:

2022-04-27  Martin Jambor  <mjambor@suse.cz>

	PR ipa/100413
	* g++.dg/ipa/pr100413.C: New test.