analyzer: eliminate sm_context::warn_for_state in favor of a new 'warn' vfunc

analyzer: eliminate sm_context::warn_for_state in favor of a new 'warn' vfunc

This patch is yet more preliminary work towards generalizing sm-malloc.cc
beyond just malloc/free.

It eliminates sm_context::warn_for_state in terms of a new sm_context::warn
vfunc, guarded by sm_context::get_state calls.

gcc/analyzer/ChangeLog:
	* diagnostic-manager.cc
	(null_assignment_sm_context::warn_for_state): Replace with...
	(null_assignment_sm_context::warn): ...this.
	* engine.cc (impl_sm_context::warn_for_state): Replace with...
	(impl_sm_context::warn): ...this.
	* sm-file.cc (fileptr_state_machine::on_stmt): Replace
	warn_for_state and on_transition calls with a get_state
	test guarding warn and set_next_state calls.
	* sm-malloc.cc (malloc_state_machine::on_stmt): Likewise.
	* sm-pattern-test.cc (pattern_test_state_machine::on_condition):
	Replace warn_for_state call with warn call.
	* sm-sensitive.cc
	(sensitive_state_machine::warn_for_any_exposure): Replace
	warn_for_state call with a get_state test guarding a warn call.
	* sm-signal.cc (signal_state_machine::on_stmt): Likewise.
	* sm-taint.cc (taint_state_machine::on_stmt):  Replace
	warn_for_state and on_transition calls with a get_state
	test guarding warn and set_next_state calls.
	* sm.h (sm_context::warn_for_state): Replace with...
	(sm_context::warn): ...this.