[libc++] Add missing #include in C11 features tests

[ldionne]

Summary

These #includes are quite important, since otherwise any

#if TEST_STD_VER > 14 && defined(TEST_HAS_C11_FEATURES)

checks are always false, and so we don't actually test for C11 support
in the standard library.

[hiraditya]

Good catch!

libcxx/trunk/test/libcxx/language.support/has_c11_features.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++98, c++03, c++11, c++14
 
 //  We have two macros for checking whether or not the underlying C library
 //   has C11 features:
 //    TEST_HAS_C11_FEATURES    - which is defined in "test_macros.h"
 //    _LIBCPP_HAS_C11_FEATURES - which is defined in <__config>
 //  They should always be the same
 
+#include <__config>
+#include "test_macros.h"
+
 #ifdef TEST_HAS_C11_FEATURES
 # ifndef _LIBCPP_HAS_C11_FEATURES
 #  error "TEST_HAS_C11_FEATURES is defined, but _LIBCPP_HAS_C11_FEATURES is not"
 # endif
 #endif
 
 #ifdef _LIBCPP_HAS_C11_FEATURES
 # ifndef TEST_HAS_C11_FEATURES
 #  error "_LIBCPP_HAS_C11_FEATURES is defined, but TEST_HAS_C11_FEATURES is not"
 # endif
 #endif
 
 int main() {}

libcxx/trunk/test/std/depr/depr.c.headers/float_h.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
  // test <float.h>
 
 #include <float.h>
 
+#include "test_macros.h"
+
 #ifndef FLT_ROUNDS
 #error FLT_ROUNDS not defined
 #endif
 
 #ifndef FLT_EVAL_METHOD
 #error FLT_EVAL_METHOD not defined
 #endif
 

libcxx/trunk/test/std/language.support/support.limits/c.limits/cfloat.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
  // test cfloat
 
 #include <cfloat>
 
+#include "test_macros.h"
+
 #ifndef FLT_ROUNDS
 #error FLT_ROUNDS not defined
 #endif
 
 #ifndef FLT_EVAL_METHOD
 #error FLT_EVAL_METHOD not defined
 #endif