[committed] coroutines, testsuite: Fix symmetric-transfer-00-basic.C on Linux.

[Iain Sandoe]

Hi.

I failed to comment out some test printing before committing the testcase.
However, for that to work, we need to include <cstdio> on Linux platforms.

tested on x86_64-linux-gnu, applied to master.
thanks
Iain
    
2020-03-27  Iain Sandoe  <i...@sandoe.co.uk>
    
        * g++.dg/coroutines/torture/symmetric-transfer-00-basic.C:
        Add <cstdio>.

diff --git 
a/gcc/testsuite/g++.dg/coroutines/torture/symmetric-transfer-00-basic.C 
b/gcc/testsuite/g++.dg/coroutines/torture/symmetric-transfer-00-basic.C
index c445fc55a2c..864846e365c 100644
--- a/gcc/testsuite/g++.dg/coroutines/torture/symmetric-transfer-00-basic.C
+++ b/gcc/testsuite/g++.dg/coroutines/torture/symmetric-transfer-00-basic.C
@@ -18,7 +18,8 @@ namespace coro = std::experimental;
 
 #include <chrono>
 #include <thread>
- 
+#include <cstdio>
+
 template <typename T> 
 struct Loopy {
   struct promise_type;
@@ -84,7 +85,7 @@ pingpong (const char *id)
       v = co_await aw;
       //fprintf (stderr, "%s = %d\n", id, v);
     }
- fprintf (stderr, "%s = %d\n", id, v);
+ //fprintf (stderr, "%s = %d\n", id, v);
 }
 
 int main ()