[libc++] Granularize the rest of memory

Reviewed By: ldionne, #libc

Spies: libcxx-commits, mgorny

Differential Revision: https://reviews.llvm.org/D132790

libcxx/test/std/strings/basic.string/string.capacity/max_size.pass.cpp

@@ -20,6 +20,7 @@
 
 #include <string>
 #include <cassert>
+#include <new>
 
 #include "test_macros.h"
 #include "min_allocator.h"