[libc++] [test] Add missing required headers to midpoint.integer.pass.cpp

This change authored by Paolo Torres <t-pator@microsoft.com>

llvm-svn: 358698
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.ops.midpoint/midpoint.integer.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.ops.midpoint/midpoint.integer.pass.cpp
index 32d931b..1956c97 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.ops.midpoint/midpoint.integer.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.ops.midpoint/midpoint.integer.pass.cpp
@@ -13,6 +13,8 @@
 // _Tp midpoint(_Tp __a, _Tp __b) noexcept
 //
 
+#include <stdint.h>
+#include <limits>
 #include <numeric>
 #include <cassert>
 #include "test_macros.h"