Revert "Use StringRef in Support/Darf APIs (NFC)"

This reverts commit r283275, it broke LLDB Android debug server.

llvm-svn: 283278
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp b/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
index 9aa3a2b..8ae0543 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
@@ -61,14 +61,12 @@
   SmallVector<DWARFFormValue, 3> AtomForms;
   for (const auto &Atom: HdrData.Atoms) {
     OS << format("Atom[%d] Type: ", i++);
-    auto TypeString = dwarf::AtomTypeString(Atom.first);
-    if (!TypeString.empty())
+    if (const char *TypeString = dwarf::AtomTypeString(Atom.first))
       OS << TypeString;
     else
       OS << format("DW_ATOM_Unknown_0x%x", Atom.first);
     OS << " Form: ";
-    auto FormString = dwarf::FormEncodingString(Atom.second);
-    if (!FormString.empty())
+    if (const char *FormString = dwarf::FormEncodingString(Atom.second))
       OS << FormString;
     else
       OS << format("DW_FORM_Unknown_0x%x", Atom.second);