src: fix NODE_DEPRECATED macro with old compilers

The `__attribute__((deprecated("warning")))` macro didn't exist until
gcc 4.5 and clang 2.9.

While io.js does not build with compilers that old, add-ons do.  Let's
make src/node.h compatible with such compilers, it's a public header.

PR-URL: https://github.com/iojs/io.js/pull/1626
Refs: https://github.com/iojs/io.js/issues/1619


Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>