[Driver] Pass Default=false to hasFlag.

I forgot to do this in r326530.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@327204 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 43e0507fd76635a074d75b91efcef369706c6691)
2 files changed