analyzer: fix ICE due to sm-state origin being purged (PR 93382)

analyzer: fix ICE due to sm-state origin being purged (PR 93382)

The ICE in PR analyzer/93382 is a validation error.

The global variable "idx" acquires a "tainted" state from local array
n1[0].  When the frame is popped, the svalue for n1[0] is purged, but
the "taint" sm_state_map's entry for "idx" has a svalue_id referencing
the now-purged svalue.  This is caught by program_state::validate as an
assertion failure.

This patch fixes the issue by resetting the origin id within
sm_state_map entries for the case where the origin id has been purged.

gcc/analyzer/ChangeLog:
	PR analyzer/93382
	* program-state.cc (sm_state_map::on_svalue_purge): If the
	entry survives, but the origin is being purged, then reset the
	origin to null.

gcc/testsuite/ChangeLog:
	PR analyzer/93382
	* gcc.dg/analyzer/pr93382.c: New test.