Fix unused function build error in lld

The lld-x86_64-darwin13 is failing with:
 error: unused function 'operator<<'

Wrap the declation in ifndef NDEBUG, which matches
what is done in MipsELFObjectWriter.cpp.

Differential Revision: https://reviews.llvm.org/D34384

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305771 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed