AK: Have AK/kmalloc.h #include <new> on other platforms

This should make stuff like placement new work correctly when building
outside of Serenity. This stuff is a bit delicate due to the weirdly
staged toolchain build at the moment. Hopefully we can unify this stuff
in the future.

AK/StringImpl.cpp

@@ -29,10 +29,6 @@
 #include "StdLibExtras.h"
 #include "kmalloc.h"
 
-#ifndef __serenity__
-#include <new>
-#endif
-
 //#define DEBUG_STRINGIMPL
 
 #ifdef DEBUG_STRINGIMPL

AK/kmalloc.h

@@ -26,6 +26,10 @@
 
 #pragma once
 
+#ifndef __serenity__
+#    include <new>
+#endif
+
 #ifdef KERNEL
 #    define AK_MAKE_ETERNAL                                               \
     public:                                                               \