[Driver] Remove the using namespace directives from headers

This adds a bunch of llvm::opt name specifiers to all the uses of types
from that namespace.

Reviewers: espindola

Differential Revision: http://llvm-reviews.chandlerc.com/D983

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184079 91177308-0d34-0410-b5e6-96231b3b80d8