Revert "Reapply "[DWARFv5] Emit file 0 to the line table.""

Revert "Reapply "[DWARFv5] Emit file 0 to the line table.""

This reverts commit r326839.

r326839 breaks assembly file parsing:

$ cat q.c
void g() {}
$ clang -S q.c -g
$ clang -g -c q.s
q.s:9:2: error: file number already allocated
     .file   1 "/tmp/test" "q.c"
     ^

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326902 91177308-0d34-0410-b5e6-96231b3b80d8