Fixing warnings under GCC4 in preparation to enable -Werror there as well:

* Replaced the use of offsetof() for structs that aren't PODs. Add a
  offset_of_member() macro to util/khash.h because that's what it's used for
  in our cases.
* Change the signature of add_debugger_command()/remove_debugger_command() on
  GCC > 2 to avoid the depricated conversion from string constants to char *.
* Adding some "suggested" parenthesis. I know that not everyone likes that, but
  it pointed out at least one bug that is fixed here as well.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@29113 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/os/drivers/KernelExport.h

@@ -174,9 +174,16 @@ extern void			panic(const char *format, ...) _PRINTFLIKE(1, 2);
 extern void			kernel_debugger(const char *message);
 extern uint64		parse_expression(const char *string);
 
+#if __GNUC__ > 2
+extern int			add_debugger_command(const char *name,
+						debugger_command_hook hook, const char *help);
+extern int			remove_debugger_command(const char *name,
+						debugger_command_hook hook);
+#else
 extern int			add_debugger_command(char *name, debugger_command_hook hook, char *help);
 extern int			remove_debugger_command(char *name,
 						debugger_command_hook hook);
+#endif
 
 /* Miscellaneous */
 extern void			spin(bigtime_t microseconds);