Add one more flag needed to build icu using clang on mac.
diff --git a/icu.gyp b/icu.gyp
index f798552..01f94b7 100644
--- a/icu.gyp
+++ b/icu.gyp
@@ -305,6 +305,7 @@
               ],
               'xcode_settings': {
                 'WARNING_CFLAGS': [
+                  '-Wno-deprecated-declarations',
                   '-Wno-dynamic-class-memaccess',
                   '-Wno-switch',
                   '-Wno-tautological-compare',