build: support building io.js as a static library

One static library could not be bundled into another, that's why
it's necessary to skip `-force_load` and `--whole-archive` linker
options to build io.js itself as a static library.

`node_target_type` variable has been added to node.gyp, along
with `--enable-static` option in configure script.

Fixes: https://github.com/iojs/io.js/issues/686
PR-URL: https://github.com/iojs/io.js/pull/1341


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>