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/stringpool.ll b/llvm/test/DebugInfo/X86/stringpool.ll
index 8df281d..d9604de 100644
--- a/llvm/test/DebugInfo/X86/stringpool.ll
+++ b/llvm/test/DebugInfo/X86/stringpool.ll
@@ -5,7 +5,7 @@
 
 !llvm.dbg.cu = !{!0}
 
-!0 = metadata !{i32 786449, metadata !8, i32 12, metadata !"clang version 3.1 (trunk 143009)", i1 true, metadata !"", i32 0, metadata !1, metadata !1, metadata !1, metadata !3, metadata !""} ; [ DW_TAG_compile_unit ]
+!0 = metadata !{i32 786449, metadata !8, i32 12, metadata !"clang version 3.1 (trunk 143009)", i1 true, metadata !"", i32 0, 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 720948, i32 0, null, metadata !"yyyy", metadata !"yyyy", metadata !"", metadata !6, i32 1, metadata !7, i32 0, i32 1, i32* @yyyy, null} ; [ DW_TAG_variable ]