weakjack.h stuff backported from jack1.

git-svn-id: http://subversion.jackaudio.org/jack/jack2/trunk/jackmp@3882 0c269be4-1314-0410-8aa9-9f06e86f4224

common/jack/weakjack.h

+/*
+    Copyright (C) 2010 Paul Davis
+    
+    This program 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.
+    
+    This program 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 this program; if not, write to the Free Software 
+    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+*/
+
+#ifndef __weakjack_h__
+#define __weakjack_h__
+
+#ifndef JACK_OPTIONAL_WEAK_EXPORT
+/* JACK_OPTIONAL_WEAK_EXPORT needs to be a macro which
+   expands into a compiler directive. If non-null, the directive 
+   must tell the compiler to arrange for weak linkage of 
+   the symbol it used with. For this to work fully may
+   require linker arguments for the client as well.
+*/
+#ifdef __GNUC__
+#define JACK_OPTIONAL_WEAK_EXPORT __attribute__((__weak__))
+#else
+/* Add other things here for non-gcc platforms */
+#endif
+#endif
+
+#ifndef JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT
+/* JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT needs to be a macro
+   which expands into a compiler directive. If non-null, the directive
+   must tell the compiler to arrange for weak linkage of the
+   symbol it is used with AND optionally to mark the symbol
+   as deprecated. For this to work fully may require
+   linker arguments for the client as well.
+*/
+#ifdef __GNUC__
+#define JACK_OPTIONAL_WEAK_DEPRECATED_EXPORT __attribute__((__weak__,__deprecated__))
+#else
+/* Add other things here for non-gcc platforms */
+#endif
+#endif
+
+#endif /* weakjack */