Correct declaration

Author: skef

c/addfeatures/main.cpp

@@ -27,7 +27,7 @@
 static char *progname; /* Program name */
 static cbCtx cbctx;    /* Client callback context */
 
-CTL_CDECL char *FDK_VERSION = "unknown";  // This variable lives here
+extern "C" char *FDK_VERSION = "unknown";  // This variable lives here
 
 /* Conversion data */
 static struct {