Pass -fvisibility=hidden on Fuchsia

This fixes an issue introduced in https://crrev.com/c/2250687, where
Fuchsia was mistakenly excluded from an if block.

Change-Id: I50f91ae6680ff582808ea064636de2ceca134f51
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2427043
Reviewed-by: Stuart Morgan <stuartmorgan@chromium.org>
Reviewed-by: Frank Tang <ftang@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 773df00..7400809 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -134,7 +134,7 @@
 # Config used to set default visibility to hidden.
 config("visibility_hidden") {
   cflags = []
-  if (is_mac || is_linux || is_chromeos || is_android) {
+  if (is_mac || is_linux || is_chromeos || is_android || is_fuchsia) {
     cflags += [ "-fvisibility=hidden" ]
   }
 }