build: fix icu-small build with ICU 72.1

- RTTI is needed for genrb now.

Fixes: #45174
PR-URL: #45195
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>

tools/icu/icu-generic.gyp

@@ -419,7 +419,7 @@
       'target_name': 'genrb',
       'type': 'executable',
       'toolsets': [ 'host' ],
-      'dependencies': [ 'icutools' ],
+      'dependencies': [ 'icutools', 'icu_implementation' ],
       'sources': [
         '<@(icu_src_genrb)'
       ],