Refactor filename/directory in DICompileUnit into a DIFile

This is the next step towards making the metadata for DIScopes have a common
prefix rather than having to delegate based on their tag type.

llvm-svn: 176913
diff --git a/llvm/test/DebugInfo/X86/vector.ll b/llvm/test/DebugInfo/X86/vector.ll
index ba58454..787b152 100644
--- a/llvm/test/DebugInfo/X86/vector.ll
+++ b/llvm/test/DebugInfo/X86/vector.ll
@@ -11,7 +11,7 @@
 
 !llvm.dbg.cu = !{!0}
 
-!0 = metadata !{i32 786449, i32 0, i32 12, metadata !"foo.c", metadata !"/Users/echristo", metadata !"clang version 3.3 (trunk 171825) (llvm/trunk 171822)", i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !1, metadata !3, metadata !""} ; [ DW_TAG_compile_unit ] [/Users/echristo/foo.c] [DW_LANG_C99]
+!0 = metadata !{i32 786449, i32 0, i32 12, metadata !6, metadata !"clang version 3.3 (trunk 171825) (llvm/trunk 171822)", i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !1, metadata !3, metadata !""} ; [ DW_TAG_compile_unit ] [/Users/echristo/foo.c] [DW_LANG_C99]
 !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, <4 x i32>* @a, null} ; [ DW_TAG_variable ] [a] [line 3] [def]