Finish bringing file_type to the llvm style (other than its name).

I assume that the name is file_type because it is the name of a c++11 type that
we will use once we convert, but at least our current implementation can look
like llvm code.

Thanks to David Blakie for the push.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200354 91177308-0d34-0410-b5e6-96231b3b80d8