bug#11986: 24.1; cc-mode not font lock objc methods with leading _

[Leo]

Put the following objc method declaration¹ in an objc-mode buffer:

    - (DDMathStringToken *)_parseNumberWithError:(NSError **)error;

You can see _parseNumberWithError not highlighted in
font-lock-function-name-face. This may be due to c-symbol-start not
containing _.

Leo

Footnotes: 
¹  Taken from https://github.com/davedelong/DDMathParser