NFC: DebugInfo: Track the origin CU rather than just the base address for range lists

Turns out knowing more than just the base address might be useful -
specifically a future change to respect a DICompileUnit flag for the use
of base address specifiers in DWARF < 5.

llvm-svn: 346380
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 2807734..070b8fe 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2275,7 +2275,8 @@
   for (const RangeSpan &Range : List.getRanges())
     SectionRanges[&Range.getStart()->getSection()].push_back(&Range);
 
-  const MCSymbol *CUBase = List.getBaseAddress();
+  const DwarfCompileUnit &CU = List.getCU();
+  const MCSymbol *CUBase = CU.getBaseAddress();
   bool BaseIsSet = false;
   for (const auto &P : SectionRanges) {
     // Don't bother with a base address entry if there's only one range in