Make WebCore compile with libc++ (Part 1)

Make WebCore compile with libc++ (Part 1)
https://bugs.webkit.org/show_bug.cgi?id=78974

Reviewed by Anders Carlsson.

Add a workaround for <rdar://problem/10858112>, which cause the standard heap functions
not to work when using an iterator with proxy objects for reference and pointer types.

* WebCorePrefix.h:
(move):
Add an overload of std::move that the heap functions can call successfully.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108174 268f45cc-cd09-0410-ab3c-d52691b4dbfc