analyzer: use std::unique_ptr for saved_diagnostic::m_stmt_finder

analyzer: use std::unique_ptr for saved_diagnostic::m_stmt_finder

gcc/analyzer/ChangeLog:
	* diagnostic-manager.cc (saved_diagnostic::saved_diagnostic): Make
	stmt_finder const.
	(saved_diagnostic::~saved_diagnostic): Remove explicit delete of
	m_stmt_finder.
	(diagnostic_manager::add_diagnostic): Make stmt_finder const.
	* diagnostic-manager.h (saved_diagnostic::saved_diagnostic):
	Likewise.
	(saved_diagnostic::m_stmt_finder): Convert to std::unique_ptr.
	(diagnostic_manager::add_diagnostic): Make stmt_finder const.
	* engine.cc (impl_sm_context::impl_sm_context): Likewise.
	(impl_sm_context::m_stmt_finder): Likewise.
	(leak_stmt_finder::clone): Convert return type to std::unique_ptr.
	* exploded-graph.h (stmt_finder::clone): Likewise.

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