YAMLIO: Allow scalars to dictate quotation rules

Introduce ScalarTraits::mustQuote which determines whether or not a
StringRef needs quoting before it is acceptable to output.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205955 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Object/YAML.h

@@ -108,6 +108,7 @@ template <> struct ScalarTraits<object::yaml::BinaryRef> {
   static void output(const object::yaml::BinaryRef &, void *,
                      llvm::raw_ostream &);
   static StringRef input(StringRef, void *, object::yaml::BinaryRef &);
+  static bool mustQuote(StringRef S) { return needsQuotes(S); }
 };
 }