c++, contracts: Only check contracts attributes [PR116607].

c++, contracts: Only check contracts attributes [PR116607].

The ICE described in the PR is caused by not filtering out non-
contract attributes before making the has_active_contract_condition
test.  Fixed, as suggested by Andrew Pinski, by just using the
existing CONTRACT_CHAIN () macro to advance through the list.

	PR c++/116607

gcc/cp/ChangeLog:

	* contracts.cc (has_active_contract_condition): Use the
	CONTRACT_CHAIN macro to advance through the attribute list.

gcc/testsuite/ChangeLog:

	* g++.dg/contracts/pr116607.C: New test.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>