Use the upstream version of libwebp, v0.4.3.

third_party/libwebp/webp/config.h

Index: third_party/libwebp/webp/config.h
diff --git a/third_party/libwebp/webp/config.h b/third_party/libwebp/webp/config.h
new file mode 100644
index 0000000000000000000000000000000000000000..62ade94d2af2a29be0a79c55271c6c42f017867b
--- /dev/null
+++ b/third_party/libwebp/webp/config.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright 2015 Google, Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+// FIXME: Workaround for skbug.com/4037
+// Some of our test machines have an older version of clang that does not
+// have
+//    __builtin_bswap16
+//
+// But libwebp expects the builtin. We can change that by using this config.h
+// file, which replaces the checks in endian_inl.h to decide whether we have
+// particular builtins.
+
+#ifdef __builtin_bswap64(x)
+    #define HAVE_BUILTIN_BSWAP64
+#endif
+
+#ifdef __builtin_bswap32(x)
+    #define HAVE_BUILTIN_BSWAP32
+#endif
+
+#ifdef __builtin_bswap16(x)
+    #define HAVE_BUILTIN_BSWAP16
+#endif