[libc++] Use uninitialized algorithms for vector

Reviewed By: ldionne, #libc

Spies: libcxx-commits, mgorny

Differential Revision: https://reviews.llvm.org/D128146

libcxx/include/__split_buffer

@@ -19,6 +19,7 @@
 #include <__iterator/move_iterator.h>
 #include <__memory/allocator.h>
 #include <__memory/compressed_pair.h>
+#include <__memory/swap_allocator.h>
 #include <__utility/forward.h>
 #include <memory>
 #include <type_traits>