[llvm-nm] Write "no symbol" output to stderr

This matches the output of binutils' nm and ensures that any scripts
or tools that use nm and expect empty output in case there no symbols
don't break.

Differential Revision: https://reviews.llvm.org/D52943

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343887 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed