leak-detective: Use callback functions to report leaks and usage information

This is more flexible than printing reports to a FILE.

src/libstrongswan/utils/backtrace.h

@@ -21,12 +21,12 @@
 #ifndef BACKTRACE_H_
 #define BACKTRACE_H_
 
+typedef struct backtrace_t backtrace_t;
+
 #include <stdio.h>
 
 #include <library.h>
 
-typedef struct backtrace_t backtrace_t;
-
 /**
  * A backtrace registers the frames on the stack during creation.
  */