Update debug info test cases with empty SplitDebugFilename field.

This could be 'null' or the empty string, DIDescriptor::getStringField
coalesces the two cases anyway so it's just a matter of legible/efficient
representation.

The change in behavior of the DICompileUnit::get* functions could be
subsumed by the full verification check - but ideally that should just be an
assertion if we could front-load the actual debug info metadata failure paths.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176907 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/DebugInfo/X86/empty-array.ll b/test/DebugInfo/X86/empty-array.ll
index e4ec4bc..4d8c025 100644
--- a/test/DebugInfo/X86/empty-array.ll
+++ b/test/DebugInfo/X86/empty-array.ll
@@ -24,7 +24,7 @@
 
 !llvm.dbg.cu = !{!0}
 
-!0 = metadata !{i32 786449, i32 0, i32 4, metadata !"t.cpp", metadata !"/Volumes/Sandbox/llvm", metadata !"clang version 3.3 (trunk 169136)", i1 true, i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !1, metadata !3} ; [ DW_TAG_compile_unit ] [/Volumes/Sandbox/llvm/t.cpp] [DW_LANG_C_plus_plus]
+!0 = metadata !{i32 786449, i32 0, i32 4, metadata !"t.cpp", metadata !"/Volumes/Sandbox/llvm", metadata !"clang version 3.3 (trunk 169136)", i1 true, i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !1, metadata !3, metadata !""} ; [ DW_TAG_compile_unit ] [/Volumes/Sandbox/llvm/t.cpp] [DW_LANG_C_plus_plus]
 !1 = metadata !{i32 0}
 !3 = metadata !{metadata !5}
 !5 = metadata !{i32 786484, i32 0, null, metadata !"a", metadata !"a", metadata !"", metadata !6, i32 1, metadata !7, i32 0, i32 1, %class.A* @a, null} ; [ DW_TAG_variable ] [a] [line 1] [def]