Do not build SkGifCodec when building SkWuffsCodec

Bug: skia:8235
Bug: https://github.com/flutter/flutter/issues/23838

Make SkGifCodec + SkGifImageReader an optional component that is not
built when skia_use_wuffs is true.

Change-Id: Ief488ec6ed929e62f73b51b3a2e993d704d2493c
Reviewed-on: https://skia-review.googlesource.com/c/187782
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index eb191dd..d2b1407 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -681,6 +681,14 @@
   }
 }
 
+optional("gif") {
+  enabled = !skia_use_wuffs
+  sources = [
+    "src/codec/SkGifCodec.cpp",
+    "third_party/gif/SkGifImageReader.cpp",
+  ]
+}
+
 optional("heif") {
   enabled = skia_use_libheif
   public_defines = [ "SK_HAS_HEIF_LIBRARY" ]
@@ -888,6 +896,7 @@
     ":fontmgr_fontconfig",
     ":fontmgr_fuchsia",
     ":fontmgr_wasm",
+    ":gif",
     ":heif",
     ":hsw",
     ":jpeg",
@@ -934,7 +943,6 @@
     "src/codec/SkCodecImageGenerator.cpp",
     "src/codec/SkColorTable.cpp",
     "src/codec/SkEncodedInfo.cpp",
-    "src/codec/SkGifCodec.cpp",
     "src/codec/SkMaskSwizzler.cpp",
     "src/codec/SkMasks.cpp",
     "src/codec/SkSampledCodec.cpp",
@@ -952,7 +960,6 @@
     "src/sfnt/SkOTUtils.cpp",
     "src/utils/mac/SkStream_mac.cpp",
     "third_party/etc1/etc1.cpp",
-    "third_party/gif/SkGifImageReader.cpp",
   ]
 
   defines = []