re-add SkDebug_stdio for Fuchsia builds

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2331383004

Review-Url: https://codereview.chromium.org/2331383004
diff --git a/BUILD.gn b/BUILD.gn
index 7b506e4..258bf2d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -511,7 +511,10 @@
   }
 
   if (is_fuchsia) {
-    sources += [ "src/gpu/gl/GrGLCreateNativeInterface_none.cpp" ]
+    sources += [
+      "src/gpu/gl/GrGLCreateNativeInterface_none.cpp",
+      "src/ports/SkDebug_stdio.cpp",
+    ]
   }
 }