IR: Move MDLocation into place

This commit moves `MDLocation`, finishing off PR21433.  There's an
accompanying clang commit for frontend testcases.  I'll attach the
testcase upgrade script I used to PR21433 to help out-of-tree
frontends/backends.

This changes the schema for `DebugLoc` and `DILocation` from:

    !{i32 3, i32 7, !7, !8}

to:

    !MDLocation(line: 3, column: 7, scope: !7, inlinedAt: !8)

Note that empty fields (line/column: 0 and inlinedAt: null) don't get
printed by the assembly writer.

llvm-svn: 226048
diff --git a/llvm/test/DebugInfo/X86/array2.ll b/llvm/test/DebugInfo/X86/array2.ll
index 6dfa8d7..5b21188 100644
--- a/llvm/test/DebugInfo/X86/array2.ll
+++ b/llvm/test/DebugInfo/X86/array2.ll
@@ -92,16 +92,16 @@
 !17 = !{i32 1, !"Debug Info Version", i32 2}
 !18 = !{!"clang version 3.5.0 "}
 !19 = !{!"0x101\00p\0016777217\000", !4, !5, !8} ; [ DW_TAG_arg_variable ] [p] [line 1]
-!20 = !{i32 1, i32 0, !4, null}
-!21 = !{i32 2, i32 0, !4, null}
-!22 = !{i32 3, i32 0, !4, null}
+!20 = !MDLocation(line: 1, scope: !4)
+!21 = !MDLocation(line: 2, scope: !4)
+!22 = !MDLocation(line: 3, scope: !4)
 !23 = !{!"0x101\00argc\0016777221\000", !10, !5, !9} ; [ DW_TAG_arg_variable ] [argc] [line 5]
-!24 = !{i32 5, i32 0, !10, null}
+!24 = !MDLocation(line: 5, scope: !10)
 !25 = !{!"0x101\00argv\0033554437\000", !10, !5, !13} ; [ DW_TAG_arg_variable ] [argv] [line 5]
 !26 = !{!"0x100\00array\006\000", !10, !5, !27} ; [ DW_TAG_auto_variable ] [array] [line 6]
 !27 = !{!"0x1\00\000\00128\0032\000\000", null, null, !9, !28, i32 0, null, null, null} ; [ DW_TAG_array_type ] [line 0, size 128, align 32, offset 0] [from int]
 !28 = !{!29}
 !29 = !{!"0x21\000\004"}        ; [ DW_TAG_subrange_type ] [0, 3]
-!30 = !{i32 6, i32 0, !10, null}
-!31 = !{i32 7, i32 0, !10, null}
-!32 = !{i32 8, i32 0, !10, null}
+!30 = !MDLocation(line: 6, scope: !10)
+!31 = !MDLocation(line: 7, scope: !10)
+!32 = !MDLocation(line: 8, scope: !10)