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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214939 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -2199,6 +2199,7 @@ void DwarfDebug::emitDebugLoc() {
   for (const auto &DebugLoc : DotDebugLocEntries) {
     Asm->OutStreamer.EmitLabel(DebugLoc.Label);
     const DwarfCompileUnit *CU = DebugLoc.CU;
+    assert(!CU->getRanges().empty());
     for (const auto &Entry : DebugLoc.List) {
       // Set up the range. This range is relative to the entry point of the
       // compile unit. This is a hard coded 0 for low_pc when we're emitting