PR analyzer/93374 reports an ICE within state_change::validate due to an
m_new_sid in a recorded state-change being out of range of the svalues
of the region_model of the new state.

During get_or_create_node we attempt to merge the new state with the
state of each of the existing enodes at the program point (in the
absence of sm-state differences), simplifying the state at each
attempt, and potentially reusing a node if we get a match.

This state-merging invalidates any svalue_ids within any state_change
object.

The root cause is that, although the code was purging any such
svalue_ids for the case where no match was found during merging, it was
failing to purge them for the case where a matching enode *was* found
for the merged state, leading to an invalid state_change along the
exploded_edge to the reused enode.

This patch moves the invalidation code to cover both cases, fixing the
ICE.  It also extends state_change validation so that states are also
checked.

gcc/analyzer/ChangeLog:
	PR analyzer/93374
	* engine.cc (exploded_edge::exploded_edge): Add ext_state param
	and pass it to change.validate.
	(exploded_graph::get_or_create_node): Move purging of change
	svalues to also cover the case of reusing an existing enode.
	(exploded_graph::add_edge): Pass m_ext_state to exploded_edge's
	ctor.
	* exploded-graph.h (exploded_edge::exploded_edge): Add ext_state
	param.
	* program-state.cc (state_change::sm_change::validate): Likewise.
	Assert that m_sm_idx is sane.  Use ext_state to validate
	m_old_state and m_new_state.
	(state_change::validate): Add ext_state param and pass it to
	the sm_change validate calls.
	* program-state.h (state_change::sm_change::validate): Add
	ext_state param.
	(state_change::validate): Likewise.

gcc/testsuite/ChangeLog:
	PR analyzer/93374
	* gcc.dg/analyzer/torture/pr93374.c: New test.