VALGRIND_* macros that don't return a value generate lots of warnings with gcc 4.6 new errors. Here is a patch I applied in Debian that shuts up most of them. You may want to adapt them so that __attribute__() gets defined to nothing on !gcc compilers though.
Created attachment 59883 [details] proposed patch
A patch that fixes all gcc 4.6 and some gcc 4.5 warnings is attached to #269778. *** This bug has been marked as a duplicate of bug 269778 ***