[DWARF][NFC] Add constants for reserved values of an initial length field.

Differential Revision: https://reviews.llvm.org/D65039

llvm-svn: 366887
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp b/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp
index e38e706..6fee080 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp
@@ -26,7 +26,7 @@
                        SectionName.data(), *OffsetPtr);
   // TODO: Add support for DWARF64.
   HeaderData.Length = Data.getRelocatedValue(4, OffsetPtr);
-  if (HeaderData.Length == 0xffffffffu)
+  if (HeaderData.Length == dwarf::DW_LENGTH_DWARF64)
     return createStringError(errc::not_supported,
                        "DWARF64 is not supported in %s at offset 0x%" PRIx32,
                        SectionName.data(), HeaderOffset);