This change lets grok_op_properties print its useful "ISO C++ prohibits
overloading operator ?:" message instead of the cryptic error message about
a missing type-specifier before '?' token.

2019-11-06  Matthias Kretz  <m.kretz@gsi.de>

	* parser.c (cp_parser_operator): Parse operator?: as an
	attempt to overload the conditional operator.

From-SVN: r277887