Revert "Revert "PR14606: debug info imported_module support""

This reverts commit r179840 with a fix to test/DebugInfo/two-cus-from-same-file.ll

I'm not sure why that test only failed on ARM & MIPS and not X86 Linux, even
though the debug info was clearly invalid on all of them, but this ought to fix
it.

llvm-svn: 179996
diff --git a/llvm/test/DebugInfo/X86/objc-fwd-decl.ll b/llvm/test/DebugInfo/X86/objc-fwd-decl.ll
index 1847d2c..3070ff8 100644
--- a/llvm/test/DebugInfo/X86/objc-fwd-decl.ll
+++ b/llvm/test/DebugInfo/X86/objc-fwd-decl.ll
@@ -12,7 +12,7 @@
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!9, !10, !11, !12}
 
-!0 = metadata !{i32 786449, metadata !13, i32 16, metadata !"clang version 3.1 (trunk 152054 trunk 152094)", i1 false, metadata !"", i32 2, metadata !1, metadata !1, metadata !1, metadata !3, metadata !""} ; [ DW_TAG_compile_unit ]
+!0 = metadata !{i32 786449, metadata !13, i32 16, metadata !"clang version 3.1 (trunk 152054 trunk 152094)", i1 false, metadata !"", i32 2, metadata !1, metadata !1, metadata !1, metadata !3,  metadata !3, metadata !""} ; [ DW_TAG_compile_unit ]
 !1 = metadata !{i32 0}
 !3 = metadata !{metadata !5}
 !5 = metadata !{i32 786484, i32 0, null, metadata !"a", metadata !"a", metadata !"", metadata !6, i32 3, metadata !7, i32 0, i32 1, %0** @a, null} ; [ DW_TAG_variable ]