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.

llvm-svn: 176907
diff --git a/llvm/test/DebugInfo/AArch64/variable-loc.ll b/llvm/test/DebugInfo/AArch64/variable-loc.ll
index 9a7f7db..9f67093 100644
--- a/llvm/test/DebugInfo/AArch64/variable-loc.ll
+++ b/llvm/test/DebugInfo/AArch64/variable-loc.ll
@@ -69,7 +69,7 @@
 
 !llvm.dbg.cu = !{!0}
 
-!0 = metadata !{i32 786449, i32 0, i32 12, metadata !"simple.c", metadata !"/home/timnor01/a64-trunk/build", metadata !"clang version 3.2 ", i1 true, i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !3, metadata !1} ; [ DW_TAG_compile_unit ] [/home/timnor01/a64-trunk/build/simple.c] [DW_LANG_C99]
+!0 = metadata !{i32 786449, i32 0, i32 12, metadata !"simple.c", metadata !"/home/timnor01/a64-trunk/build", metadata !"clang version 3.2 ", i1 true, i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !3, metadata !1, metadata !""} ; [ DW_TAG_compile_unit ] [/home/timnor01/a64-trunk/build/simple.c] [DW_LANG_C99]
 !1 = metadata !{i32 0}
 !3 = metadata !{metadata !5, metadata !11, metadata !14}
 !5 = metadata !{i32 786478, i32 0, metadata !6, metadata !"populate_array", metadata !"populate_array", metadata !"", metadata !6, i32 4, metadata !7, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, void (i32*, i32)* @populate_array, null, null, metadata !1, i32 4} ; [ DW_TAG_subprogram ] [line 4] [def] [populate_array]