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>

tools/icu/icu-generic.gyp

@@ -26,6 +26,9 @@
           'UCONFIG_NO_REGULAR_EXPRESSIONS=1',
           'U_ENABLE_DYLOAD=0',
           'U_STATIC_IMPLEMENTATION=1',
+          # Don't need std::string in API.
+          # Also, problematic: <http://bugs.icu-project.org/trac/ticket/11333>
+          'U_HAVE_STD_STRING=0',
           # TODO(srl295): reenable following pending
           # https://code.google.com/p/v8/issues/detail?id=3345
           # (saves some space)