PR c/23075
* c-typeck.c (c_finish_return): Set TREE_NO_WARNING on RETURN_EXPR
if "return with no value, in function returning non-void" warning
has been issued.
* tree-cfg.c (execute_warn_function_return): Don't look at
RETURN_EXPRs with TREE_NO_WARNING set.
* typeck.c (check_return_expr): Add no_warning argument. Set
*no_warning to true if "return-statement with no value, in function
returning" warning has been issued.
* cp-tree.h (check_return_expr): Adjust prototype.
* semantics.c (finish_return_stmt): Set TREE_NO_WARNING if
check_return_expr set *no_warning to true.
* gcc.dg/pr23075.c: New test.
* g++.dg/warn/pr23075.C: New test.