- Adds support for `DW_TAG_module` DIEs and recurse over their children.
Prior to this patch, entities hanging below `DW_TAG_module` were just
not visible. This DIE kind is commonly generated by Objective-C modules.
This patch will represent such entities, which will print as
```
[001] {CompileUnit} '/llvm/tools/clang/test/modules/<stdin>'
[002] {Producer} 'LLVM version 3.7.0'
{Directory} '/llvm/tools/clang/test/modules'
{File} '<stdin>'
[002] {Module} 'DebugModule'
```
The minimal test case included is just the result of
```
$ llc llvm/test/DebugInfo/X86/DIModule.ll
-accel-tables=Dwarf
-o llvm/unittests/DebugInfo/LogicalView/Inputs/test-dwarf-clang-module.o
-filetype=obj
```
cb575785b9
