llvm-dg: fix adding edge to unified return value
llvm-dg: fix adding edge to unified return value

we added edge from each basic block to the new single return value.
Add the edge only from basic blocks that are terminated with ReturnInst

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>

mchalupa/dg,mchalupa/dg,mchalupa/dg,mchalupa/dg