Adding DIImportedModules to DIScopes.

This is just the basic groundwork for supporting DW_TAG_imported_module but I
wanted to commit this before pushing support further into Clang or LLVM so that
this rather churny change is isolated from the rest of the work. The major
churn here is obviously adding another field (within the common DIScope prefix)
to all DIScopes (files, classes, namespaces, lexical scopes, etc). This should
be the last big churny change needed for DW_TAG_imported_module/using directive
support/PR14606.

llvm-svn: 178099
diff --git a/llvm/test/DebugInfo/X86/2011-09-26-GlobalVarContext.ll b/llvm/test/DebugInfo/X86/2011-09-26-GlobalVarContext.ll
index ad55db0..c19d99f 100644
--- a/llvm/test/DebugInfo/X86/2011-09-26-GlobalVarContext.ll
+++ b/llvm/test/DebugInfo/X86/2011-09-26-GlobalVarContext.ll
@@ -18,20 +18,20 @@
 
 !llvm.dbg.cu = !{!0}
 
-!0 = metadata !{i32 786449, metadata !20, i32 12, metadata !"clang version 3.0 (trunk)", i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !3, metadata !12, metadata !""} ; [ DW_TAG_compile_unit ]
+!0 = metadata !{i32 786449, metadata !20, null, i32 12, metadata !"clang version 3.0 (trunk)", i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !3, metadata !12, metadata !""} ; [ DW_TAG_compile_unit ]
 !1 = metadata !{i32 0}
 !3 = metadata !{metadata !5}
-!5 = metadata !{i32 720942, metadata !6, metadata !6, metadata !"f", metadata !"f", metadata !"", i32 3, metadata !7, i1 false, i1 true, i32 0, i32 0, i32 0, i32 0, i1 false, i32 ()* @f, null, null, metadata !10} ; [ DW_TAG_subprogram ]
-!6 = metadata !{i32 720937, metadata !20} ; [ DW_TAG_file_type ]
-!7 = metadata !{i32 720917, i32 0, metadata !"", i32 0, i32 0, i64 0, i64 0, i32 0, i32 0, i32 0, metadata !8, i32 0, i32 0} ; [ DW_TAG_subroutine_type ]
+!5 = metadata !{i32 720942, metadata !6, null, metadata !6, metadata !"f", metadata !"f", metadata !"", i32 3, metadata !7, i1 false, i1 true, i32 0, i32 0, i32 0, i32 0, i1 false, i32 ()* @f, null, null, metadata !10} ; [ DW_TAG_subprogram ]
+!6 = metadata !{i32 720937, metadata !20, null} ; [ DW_TAG_file_type ]
+!7 = metadata !{i32 720917, i32 0, null, metadata !"", i32 0, i32 0, i64 0, i64 0, i32 0, i32 0, i32 0, metadata !8, i32 0, i32 0} ; [ DW_TAG_subroutine_type ]
 !8 = metadata !{metadata !9}
-!9 = metadata !{i32 720932, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ]
+!9 = metadata !{i32 720932, null, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ]
 !10 = metadata !{metadata !11}
 !11 = metadata !{i32 720932}                      ; [ DW_TAG_base_type ]
 !12 = metadata !{metadata !14}
 !14 = metadata !{i32 720948, i32 0, null, metadata !"GLB", metadata !"GLB", metadata !"", metadata !6, i32 1, metadata !9, i32 0, i32 1, i32* @GLB, null} ; [ DW_TAG_variable ]
 !15 = metadata !{i32 786688, metadata !16, metadata !"LOC", metadata !6, i32 4, metadata !9, i32 0, i32 0} ; [ DW_TAG_auto_variable ]
-!16 = metadata !{i32 786443, metadata !20, metadata !5, i32 3, i32 9, i32 0} ; [ DW_TAG_lexical_block ]
+!16 = metadata !{i32 786443, metadata !20, null, metadata !5, i32 3, i32 9, i32 0} ; [ DW_TAG_lexical_block ]
 !17 = metadata !{i32 4, i32 9, metadata !16, null}
 !18 = metadata !{i32 4, i32 23, metadata !16, null}
 !19 = metadata !{i32 5, i32 5, metadata !16, null}