[committed,testsuite] Only run gcc.dg/tree-ssa/pr61144.c when aliases are supported

[FX]

All other tests in gcc.dg/ that use __attribute__((__alias__())) are guarded by 
dg-require-alias.
Let’s do the same for gcc.dg/tree-ssa/pr61144.c, otherwise it complains on 
darwin.



2014-11-15  Francois-Xavier Coudert  <fxcoud...@gcc.gnu.org>

        * gcc.dg/tree-ssa/pr61144.c: Add dg-require-alias.


 
Index: gcc.dg/tree-ssa/pr61144.c
===================================================================
--- gcc.dg/tree-ssa/pr61144.c   (revision 217599)
+++ gcc.dg/tree-ssa/pr61144.c   (working copy)
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-require-weak "" } */
+/* { dg-require-alias "" } */
 /* { dg-options "-O2 -fdump-tree-optimized" } */
 static int dummy = 0;
 extern int foo __attribute__((__weak__, __alias__("dummy")));