IR: Don't use raw_null_ostream in Verifier

While using a raw_null_ostream meant that the Verifier didn't have to
think about whether to print, it's actually quite expensive to print out
IR.  Only print if the output is going somewhere.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266884 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed