DebugInfo: Hide isScopeRef() and isTypeRef() behind NDEBUG

The copies of these in `lib/IR/DebugInfo.cpp` are apparently [1] only
used in assertions now, so hide them behind `#ifndef NDEBUG`.

[1]: http://lab.llvm.org:8011/builders/lld-x86_64-darwin13/builds/9238

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233661 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed