Compile cleanly with clang.

To compile Ardour with LLVM/clang, do the usual thing but set the CXX and CC
environment variables, e.g.:

CC=/usr/bin/clang CXX=/usr/bin/clang++ ./waf configure build


git-svn-id: svn://localhost/ardour2/branches/3.0@12418 d708f5d6-7413-0410-9779-e7cbd77b26cf

libs/surfaces/control_protocol/control_protocol/control_protocol.h

@@ -146,7 +146,8 @@ class ControlProtocol : public PBD::Stateful, public PBD::ScopedConnectionList,
 };
 
 extern "C" {
-	struct ControlProtocolDescriptor {
+	class ControlProtocolDescriptor {
+	public:
 	    const char* name;      /* descriptive */
 	    const char* id;        /* unique and version-specific */
 	    void*       ptr;       /* protocol can store a value here */