In an effort to maintain parity with the official Node.js build, which
sets `node_prefix` to `/`, this takes advantage of the `DESTDIR`
variable which changes the actual installation location used by
`make install`. Without this, it relies on the `PREFIX` which is now
explicitly set to `/`, even though it won't be installed there.
See the `install.py` script for more information, in the form of code:
2a97eb61c6/tools/install.py (L13)
/cc @benjamn
To remain the same as official Node.js releases, we need to build with
the `small-icu` ICU (International Components for Unicode) package.
For Node.js 4.x this means ICU 56.x. As found with `process.config` on
an official Node.js release.
See https://github.com/nodejs/node/wiki/Intl#configure-node-with-specific-icu-source.
