* c-decl.c (flexible_array_type_p): New function.
	(grokdeclarator, finish_struct): Use it.
	* doc/extend.texi: Document constraints on use of structures with
	flexible array members.

testsuite:
	* gcc.dg/c90-flex-array-1.c, gcc.dg/c99-flex-array-3.c,
	gcc.dg/c99-flex-array-4.c: New tests.

From-SVN: r56411