[committed] coroutines, testsuite: Require C++17 for two tests.

[Iain Sandoe]

Hi,

While the coroutines implementation, and most of the coroutines
tests, will operate with C++14 or newer, these tests require
facilities introduced in C++17.  Add the target requirement.

Tested on x86_64-darwin16,
applied to master,
thanks
Iain

gcc/testsuite/

2020-04-19  Iain Sandoe  <i...@sandoe.co.uk>
    
        * g++.dg/coroutines/torture/co-await-17-capture-comp-ref.C: Require
        C++17.
        * g++.dg/coroutines/torture/co-ret-15-default-return_void.C: Likewise.


diff --git 
a/gcc/testsuite/g++.dg/coroutines/torture/co-await-17-capture-comp-ref.C 
b/gcc/testsuite/g++.dg/coroutines/torture/co-await-17-capture-comp-ref.C
index 93a43fbd298..c5829c455a5 100644
--- a/gcc/testsuite/g++.dg/coroutines/torture/co-await-17-capture-comp-ref.C
+++ b/gcc/testsuite/g++.dg/coroutines/torture/co-await-17-capture-comp-ref.C
@@ -1,4 +1,4 @@
-//  { dg-do run }
+//  { dg-do run { target c++17 } }
 
 #include "../coro.h"
 
diff --git 
a/gcc/testsuite/g++.dg/coroutines/torture/co-ret-15-default-return_void.C 
b/gcc/testsuite/g++.dg/coroutines/torture/co-ret-15-default-return_void.C
index e600feae129..99910f33f53 100644
--- a/gcc/testsuite/g++.dg/coroutines/torture/co-ret-15-default-return_void.C
+++ b/gcc/testsuite/g++.dg/coroutines/torture/co-ret-15-default-return_void.C
@@ -1,4 +1,4 @@
-// { dg-do run }
+// { dg-do run { target c++17 } }
 //
 // Check if default return_void is insert at correct position.
 #include <cassert>