Fix SVG flag iOS linking

TBR=mtklein@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2344533002

Review-Url: https://codereview.chromium.org/2344533002
diff --git a/tools/flags/SkCommonFlags.cpp b/tools/flags/SkCommonFlags.cpp
index 57078fa..bf2bde0 100644
--- a/tools/flags/SkCommonFlags.cpp
+++ b/tools/flags/SkCommonFlags.cpp
@@ -48,6 +48,8 @@
 
 DEFINE_string(skps, "skps", "Directory to read skps from.");
 
+DEFINE_string(svgs, "", "Directory to read SVGs from, or a single SVG file.");
+
 DEFINE_int32(threads, -1, "Run threadsafe tests on a threadpool with this many extra threads, "
                           "defaulting to one extra thread per core.");