Fix r236754: Add the missing yaml-bench dir to the makefile for utils.

Fix r236754: Add the missing yaml-bench dir to the makefile for utils.

This commit adds the missing yaml-bench utility to the
makefile in utils. It was missing before and it caused
the regression tests to fail on some buildbots when llvm-lit
couldn't find yaml-bench when llvm was built without
cmake after I committed r236754.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236761 91177308-0d34-0410-b5e6-96231b3b80d8