avutil: add obj-c helpers into header-only include

Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Aman Karmani <aman@tmm1.net>

libavutil/objc.h

@@ -0,0 +1,32 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVUTIL_OBJC_H
+#define AVUTIL_OBJC_H
+
+#include <Foundation/Foundation.h>
+
+static inline void ff_objc_release(NSObject **obj)
+{
+    if (*obj) {
+        [*obj release];
+        *obj = nil;
+    }
+}
+
+#endif /* AVUTIL_OBJC_H */