analyzer: convert sm_context * to sm_context &

These are never nullptr and never change, so use a reference rather
than a pointer.

No functional change intended.

gcc/analyzer/ChangeLog:
	* diagnostic-manager.cc
	(diagnostic_manager::add_events_for_eedge): Pass sm_ctxt by
	reference.
	* engine.cc (impl_region_model_context::on_condition): Likewise.
	(impl_region_model_context::on_bounded_ranges): Likewise.
	(impl_region_model_context::on_phi): Likewise.
	(exploded_node::on_stmt): Likewise.
	* sm-fd.cc: Update all uses of sm_context * to sm_context &.
	* sm-file.cc: Likewise.
	* sm-malloc.cc: Likewise.
	* sm-pattern-test.cc: Likewise.
	* sm-sensitive.cc: Likewise.
	* sm-signal.cc: Likewise.
	* sm-taint.cc: Likewise.
	* sm.h: Likewise.
	* varargs.cc: Likewise.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/analyzer_gil_plugin.c: Update all uses of
	sm_context * to sm_context &.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>