Fix r329293:  Add a missing CMake dependency

The unittest plugin indirectly includes Attributes.gen, so make sure its
target depends on the appropriate tablegen target.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329308 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed