[NFC] Make DeclName::dump() and ObjCSelector::dump() work

They were being stripped out of builds as dead code.

Author: beccadax

include/swift/AST/Identifier.h

@@ -590,7 +590,7 @@ class DeclName {
   llvm::raw_ostream &printPretty(llvm::raw_ostream &os) const;
 
   /// Dump this name to standard error.
-  LLVM_ATTRIBUTE_DEPRECATED(void dump() const,
+  LLVM_ATTRIBUTE_DEPRECATED(void dump() const LLVM_ATTRIBUTE_USED,
                             "only for use within the debugger");
 };
 
@@ -672,7 +672,7 @@ class ObjCSelector {
   }
 
   /// Dump this selector to standard error.
-  LLVM_ATTRIBUTE_DEPRECATED(void dump() const,
+  LLVM_ATTRIBUTE_DEPRECATED(void dump() const LLVM_ATTRIBUTE_USED,
                             "only for use within the debugger");
 
   /// Compare two Objective-C selectors, producing -1 if \c *this comes before