Propagate the split dwarf file information through into the backend

Propagate the split dwarf file information through into the backend
and through to the debug info in the module. In order to make the
testcase a bit more efficient allow the filename to go through
compilation for compile and not assemble jobs and turn off the
extract for cases where we don't create an object.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175935 91177308-0d34-0410-b5e6-96231b3b80d8