Provide operator<< for stream output of DeclarationNames

ASTDumper was already trying to do this & instead got an implicit bool
conversion by surprise (thus printing out 0 or 1 instead of the name of
the declaration). To avoid that issue & simplify call sites, simply make
it the normal/expected operator<<(raw_ostream&, ...) overload & simplify
all the existing call sites. (bonus: this function doesn't need to be a
member or friend, it's just using public API in DeclarationName)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181832 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ASTDumper.cpp b/lib/AST/ASTDumper.cpp
index 340cc41..790538f 100644
--- a/lib/AST/ASTDumper.cpp
+++ b/lib/AST/ASTDumper.cpp
@@ -449,9 +449,7 @@
 
   if (const NamedDecl *ND = dyn_cast<NamedDecl>(D)) {
     ColorScope Color(*this, DeclNameColor);
-    OS << " '";
-    ND->getDeclName().printName(OS);
-    OS << "'";
+    OS << " '" << ND->getDeclName() << '\'';
   }
 
   if (const ValueDecl *VD = dyn_cast<ValueDecl>(D))