The grammar for variadic init-capture was fixed at the Prague C++ meeting
where we finalized C++20.

gcc/cp/ChangeLog
2020-02-24  Jason Merrill  <jason@redhat.com>

	P0780R2: Resolve lambda init-capture pack grammar.
	* parser.c (cp_parser_lambda_introducer): Expect &...x=y rather than
	...&x=y.