DwarfUnit: Replace unnecessary conditionals with asserts.

We used to be pretty vague about what debug entities were what, with
many conditionals to silently drop/skip/accept things. These don't seem
to be relevant anymore.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201194 91177308-0d34-0410-b5e6-96231b3b80d8
DwarfUnit: Refactor DW_AT_file creation into a common function.

This is preliminary work to fix type unit file strings so they appear in
their originating CU's line table - but it's also just good/simple
cleanup, so I'm committing it ahead of time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201195 91177308-0d34-0410-b5e6-96231b3b80d8
DwarfUnit: Provide a reference to a defining DwarfCompileUnit from DwarfTypeUnit.

Type units need to insert their file strings into the compile unit's
line/file table. This is preliminary work to that end.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201196 91177308-0d34-0410-b5e6-96231b3b80d8
Fix some formatting in my last commit (r201196)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201197 91177308-0d34-0410-b5e6-96231b3b80d8
DwarfUnit: Include type unit's file strings in the defining compile unit's file_names table

There's still one piece missing here, which is adding the
DW_AT_stmt_list to the type unit that refer's to the compile unit's line
table. Working on that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201198 91177308-0d34-0410-b5e6-96231b3b80d8