[Dominators] Don't print the whole tree when running with -debug

As the incremental API is now used in several transforms, printing
the whole dominator tree creates a lot of noise when running with
the `-debug` flag. This patch fixes that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311176 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed