Fix unittest makefile after r147425. This should unbreak the makefile

build. This didn't show up in the CMake build because the CMake build
for the unittests is rather poorly factored.

This probably isn't the correct fix. This should be a bitcode reader
unittest not a VMCore unittest. I'll move it and clean various parts of
the unittest up in a follow-up patch, but I wanted to unbreak the bots.

llvm-svn: 147427