Disable this test completely on lto systems

This test succeeds on macosx but fails on iphoneos. XFAIL does not work.
Use "REQUIRES: non_lto" instead.

rdar://26281388

Author: aschwaighofer

test/Driver/static-stdlib.swift

@@ -1,6 +1,6 @@
 // Statically link a "hello world" program
 // XFAIL: linux
-// XFAIL: lto
+// REQUIRES: non_lto
 // REQUIRES: static_stdlib
 print("hello world!")
 // RUN: rm -rf %t && mkdir %t