[PATCH, testsuite]: Fix g++.dg/lto/pr79671 execute failure

[Uros Bizjak]

Hello!

We have to match input and output operand (or use "+") of an empty asm
to move the value to a register.

2017-05-02  Uros Bizjak  <ubiz...@gmail.com>

    * g++.dg/lto/pr79671_0.C (foo): Fix asm constraints.

Tested on alphaev68-linux-gnu (where the unpatched testcase fails) and
x86_64-linux-gnu.

OK for mailine?

Uros.

Index: g++.dg/lto/pr79671_0.C
===================================================================
--- g++.dg/lto/pr79671_0.C      (revision 247497)
+++ g++.dg/lto/pr79671_0.C      (working copy)
@@ -13,7 +13,7 @@ int __attribute__((noinline)) foo()
   new (&x) B (0);
   y = x;
   B *q = reinterpret_cast <B *>(&y);
-  asm volatile ("" : "=r" (q) : "r" (q));
+  asm volatile ("" : "+r" (q));
   return q->i;
 }
 extern "C" void bar ();