Allow building icuuc/icui18n with -fvisibility=hidden

This CL adds two alternative {icuuc,icui18n}_hidden_visibility targets
which can be used to statically link against icu with default visibility
set to hidden, thereby allowing much smaller code size.

There are use cases where the build root used does not have
-fvisibility=hidden enabled but we want to enable it specifically for
individual dependencies.

Change-Id: I03c22f1f6aae63ac8cf137ab357d3117d3899be0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2236407
Reviewed-by: Frank Tang <ftang@chromium.org>
1 file changed