Compile SkJpegCodec on bzl iOS build

BUG=skia:

Change-Id: I7ffb33bc4b215874821d6797e7795e8dd59467ee
Reviewed-on: https://skia-review.googlesource.com/8312
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
diff --git a/public.bzl b/public.bzl
index b4b166f..4f063ff 100644
--- a/public.bzl
+++ b/public.bzl
@@ -254,7 +254,6 @@
     ],
     exclude = [
         "src/codec/*Ico*.cpp",
-        "src/codec/*Jpeg*.cpp",
         "src/codec/*Webp*.cpp",
         "src/codec/*Png*",
         "src/codec/*Raw*.cpp",
@@ -584,6 +583,7 @@
 DEFINES_IOS = [
     "SK_BUILD_FOR_IOS",
     "SK_BUILD_NO_OPTS",
+    "SK_HAS_JPEG_LIBRARY",
     "SK_IGNORE_ETC1_SUPPORT",
     "SKNX_NO_SIMD",
 ]