Fix #78290
* statement.cs (Return.Resolve): Move error checking to ...
* flowbranching.cs (FlowBranching.AddReturnOrigin): ... this.
(FlowBranchingException): Handle return origins like break and
continue origins.
(FlowBranching.UsageVector.CheckOutParameters): Remove.
In gmcs:
Fix #78290
* statement.cs (Return.Resolve): Move error checking to ...
* flowbranching.cs (FlowBranching.AddReturnOrigin): ... this.
(FlowBranchingException): Handle return origins like break and
continue origins.
(FlowBranching.UsageVector.CheckOutParameters): Remove.
In tests:
* test-508.cs: New test -- didn't fail earlier, but include to
catch any regressions.
In errors:
* cs0177-5.cs, cs0177-6.cs: New tests based on #78290.
svn path=/trunk/mcs/; revision=60279
