[Parser] Factor out token prefix checking. NFC.

Author: huonw

include/swift/Parse/Parser.h

@@ -517,16 +517,16 @@ class Parser {
   /// Add a camel-cased option if it is different than the first option.
   void diagnoseConsecutiveIDs(StringRef First, SourceLoc FirstLoc,
                               StringRef DeclKindName);
-     
-  /// \brief Check whether the current token starts with '<'.
-  bool startsWithLess(Token Tok) {
-    return Tok.isAnyOperator() && Tok.getText()[0] == '<';
+
+  bool startsWithSymbol(Token Tok, char symbol) {
+    return (Tok.isAnyOperator() || Tok.isPunctuation()) &&
+           Tok.getText()[0] == symbol;
   }
+  /// \brief Check whether the current token starts with '<'.
+  bool startsWithLess(Token Tok) { return startsWithSymbol(Tok, '<'); }
 
   /// \brief Check whether the current token starts with '>'.
-  bool startsWithGreater(Token Tok) {
-    return Tok.isAnyOperator() && Tok.getText()[0] == '>';
-  }
+  bool startsWithGreater(Token Tok) { return startsWithSymbol(Tok, '>'); }
 
   /// \brief Consume the starting '<' of the current token, which may either
   /// be a complete '<' token or some kind of operator token starting with '<',