c++: REF_PARENTHESIZED_P wrapper inhibiting NRVO [PR67302]

c++: REF_PARENTHESIZED_P wrapper inhibiting NRVO [PR67302]

Here, in C++14 or later, we remember the parentheses around 'a' in the
return statement by using a REF_PARENTHESIZED_P wrapper, which ends up
inhibiting NRVO because we don't look through this wrapper before
checking the conditions for NRVO.  This patch fixes this by calling
maybe_undo_parenthesized_ref sooner in check_return_expr.

	PR c++/67302

gcc/cp/ChangeLog:

	* typeck.c (check_return_expr): Call maybe_undo_parenthesized_ref
	sooner, before the NRVO handling.

gcc/testsuite/ChangeLog:

	* g++.dg/opt/nrv21.C: New test.