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