Add yaml2obj to check-lld deps, since the PECOFF tests need it

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@187165 91177308-0d34-0410-b5e6-96231b3b80d8
Use env in a pecoff test so it passes with the lit shell test runner

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@187170 91177308-0d34-0410-b5e6-96231b3b80d8