Avoid a compiler warning about int-to-ptr casting.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14480 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/mpi/libmpiwrap.c b/mpi/libmpiwrap.c
index b2a964d..a5349e0 100644
--- a/mpi/libmpiwrap.c
+++ b/mpi/libmpiwrap.c
@@ -152,7 +152,7 @@
 typedef  unsigned long  UWord;
 
 #if !defined(offsetof)
-#  define offsetof(type,memb) ((int)&((type*)0)->memb)
+#  define offsetof(type,memb) ((UWord)&((type*)0)->memb)
 #endif
 
 /* Find the size of long double image (not 'sizeof(long double)').