build: work around VS2015 issue in ICU <56

The particular ufile.c is from
http://bugs.icu-project.org/trac/changeset/37704
and should be OK for ICU 54 and 55.

Also, adds general mechanism for floating patches on top of ICU.

Fixes: https://github.com/nodejs/node/issues/2279
PR-URL: https://github.com/nodejs/node/pull/2283


Reviewed-By: João Reis <reis@janeasystems.com>