testsuite: Fix run to main issue introduced by GCC 5.x.

Adding a dummy assignment as a new breakpoint anchor because
breakpoint on return statement doesn't work for GCC 5.x.

2016-03-02  Bernhard Heckel  <bernhard.heckel@intel.com>

gdb/testsuite/Changelog:

     * gdb.cp/vla-cxx.cc: Insert dummy assignment as anchor for an breakpoint.

gdb/testsuite/ChangeLog

+2016-03-02  Bernhard Heckel  <bernhard.heckel@intel.com>
+
+	* gdb.cp/vla-cxx.cc: Insert dummy assignment as anchor for an breakpoint.
+
 2016-03-02  Bernhard Heckel  <bernhard.heckel@intel.com>
 
 	* gdb.mi/vla.f90: Nullify pointer after declaration.

gdb/testsuite/gdb.cp/vla-cxx.cc

@@ -45,5 +45,6 @@ int main(int argc, char **argv)
     vla[i] = 5 + 2 * i;
 
   // vlas_filled
+  vla[0] = 2 * vla[0];
   return vla[2];
 }