analyzer: fix feasibility false +ve with overly complex svalues

analyzer: fix feasibility false +ve with overly complex svalues

gcc/analyzer/ChangeLog:
	* diagnostic-manager.cc
	(class auto_disable_complexity_checks): New.
	(epath_finder::explore_feasible_paths): Use it to disable
	complexity checks whilst processing the worklist.
	* region-model-manager.cc
	(region_model_manager::region_model_manager): Initialize
	m_check_complexity.
	(region_model_manager::reject_if_too_complex): Bail if
	m_check_complexity is false.
	* region-model.h
	(region_model_manager::enable_complexity_check): New.
	(region_model_manager::disable_complexity_check): New.
	(region_model_manager::m_check_complexity): New.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/feasibility-3.c: New test.

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