enable llvm-nm by default for all archs

[nickdesaulniers]

printing the version doesn't provide much meaningful info:

➜  kernel-all git:(master) ✗ llvm-nm --version
LLVM (http://llvm.org/):
  LLVM version 9.0.0svn
  Optimized build.
  Default target: x86_64-unknown-linux-gnu
  Host CPU: haswell

there's no version check because we don't have a minimum required version that we know about.