build: i18n: fix build on OSX

Fix config option that doesn't work with OSX.

Fixes: https://github.com/joyent/node/issues/8521
PR-URL: https://github.com/joyent/node/pull/8602
Reviewed-by: Trevor Norris <trev.norris@gmail.com>
build: i18n: fix icu toolset dependencies

So what I did here is to make the icutools library actually contain the
entire ICU dependencies needed for host-side tools. Sadly, this will
build ICU twice, but avoids conflicts between host and target side.
This all seems like a gyp bug of some sort, but without docs for
toolsets, who’s to say?

I removed the icuio library as a separate target, because it was only
used by the host-side tools.

PR-URL: https://github.com/joyent/node/pull/8681
Reviewed-by: Trevor Norris <trev.norris@gmail.com>
build: i18n: reduce on-disk size

Reduces space by about 1MB with ICU 54 (over without this patch).
Also trims a few other source files, but only conditional on the exact ICU
version used. This is to future-proof - a file that is unneeded now may
be needed in future ICUs.