PR c++/71290 - Flexible array member is not diagnosed with -pedantic

PR c++/71290 - Flexible array member is not diagnosed with -pedantic

gcc/cp/ChangeLog:
	PR c++/71290
	* decl.c (grokdeclarator): Warn on flexible array members.

gcc/testsuite/ChangeLog:
	PR c++/71290
	* g++.dg/ext/flexarray-mangle-2.C: Adjust.
	* g++.dg/ext/flexarray-mangle.C: Same.
	* g++.dg/ext/flexarray-subst.C: Same.
	* g++.dg/ext/flexary10.C: Same.
	* g++.dg/ext/flexary11.C: Same.
	* g++.dg/ext/flexary14.C: Same.
	* g++.dg/ext/flexary16.C: Same.
	* g++.dg/ext/flexary18.C: Same.
	* g++.dg/ext/flexary19.C: Same.
	* g++.dg/ext/flexary7.C: Same.
	* gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations1.C: Same.
	* gcc/testsuite/g++.dg/ubsan/object-size-1.C: Same.
	* gcc/testsuite/obj-c++.dg/property/at-property-23.mm: Same.

From-SVN: r244910