When ICU was rolled from icu4.6 to icu52, libicudata_nacl was not rebuilt
on some build bots leading to an undefined symbol linker error (icudt52_dat
not found).

By making icudata_nacl target explicitly depend on uvernum.h, we can force
icudata_nacl target to be rebuilt when there's an ICU version change.
(a work-around suggested by Sergey).

A more fundamental fix is to change the way nacl targets determine
its dependencies See https://codereview.chromium.org/336993003/

BUG=132145
TEST=After rolling icu to 52, incremental build will not complain about missing symbol (icudt52_dat).
R=sergeyu@chromium.org

Review URL: https://codereview.chromium.org/338063002

git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/icu52@277885 4ff67af0-8c30-449e-8e8b-ad334ec8d88c