LibDriver: Silently do nothing when provided no inputs.

This behavior is strange, but it matches lib.exe. Based on a patch by
Nico Weber.

Fixes PR27335.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266236 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed