DebugInfo: Assert that any CU for which debug_loc lists are emitted, has at least one range.

This was coming in weird debug info that had variables (and hence
debug_locs) but was in GMLT mode (because it was missing the 13th field
of the compile_unit metadata) so no ranges were constructed. We should
always have at least one range for any CU with a debug_loc in it -
because the range should cover the debug_loc.

The assertion just ensures that the "!= 1" range case inside the
subsequent loop doesn't get entered for the case where there are no
ranges at all, which should never reach here in the first place.

llvm-svn: 214939
diff --git a/llvm/test/DebugInfo/ARM/PR16736.ll b/llvm/test/DebugInfo/ARM/PR16736.ll
index 8c025ad..c26f0ca 100644
--- a/llvm/test/DebugInfo/ARM/PR16736.ll
+++ b/llvm/test/DebugInfo/ARM/PR16736.ll
@@ -41,7 +41,7 @@
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!17, !21}
 
-!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.4 (trunk 190804) (llvm/trunk 190797)", i1 true, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [//<unknown>] [DW_LANG_C_plus_plus]
+!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.4 (trunk 190804) (llvm/trunk 190797)", i1 true, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !"", i32 1} ; [ DW_TAG_compile_unit ] [//<unknown>] [DW_LANG_C_plus_plus]
 !1 = metadata !{metadata !"/<unknown>", metadata !""}
 !2 = metadata !{}
 !3 = metadata !{metadata !4}