[tests] XFAIL a few things that require libc (?) support missing on Darwin.

llvm-svn: 174450
diff --git a/libcxx/test/strings/c.strings/version_cuchar.pass.cpp b/libcxx/test/strings/c.strings/version_cuchar.pass.cpp
index a18f343..fa47f0f 100644
--- a/libcxx/test/strings/c.strings/version_cuchar.pass.cpp
+++ b/libcxx/test/strings/c.strings/version_cuchar.pass.cpp
@@ -6,6 +6,8 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+//
+// XFAIL: apple-darwin
 
 // <cuchar>