[libcxx] Do not implicitly #include assert.h

Users should only get the assert() macros if they explicitly include
them.

Found after switching from the GNU C++ stdlib to the LLVM C++ stdlib.

llvm-svn: 372963
diff --git a/libcxx/test/std/experimental/simd/simd.cons/broadcast.pass.cpp b/libcxx/test/std/experimental/simd/simd.cons/broadcast.pass.cpp
index 57a6cd5..b55208a 100644
--- a/libcxx/test/std/experimental/simd/simd.cons/broadcast.pass.cpp
+++ b/libcxx/test/std/experimental/simd/simd.cons/broadcast.pass.cpp
@@ -13,8 +13,9 @@
 // [simd.class]
 // template <class U> simd(U&& value);
 
-#include <cstdint>
 #include <experimental/simd>
+#include <cstdint>
+#include <cassert>
 
 #include "test_macros.h"