Move the DIFile operand to DITypes from the 4th operand to the 2nd.

This is another step along the way to making all DIScopes have a common prefix
which can be added to in a general manner to support using directives
(DW_TAG_imported_module).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177462 91177308-0d34-0410-b5e6-96231b3b80d8