mpi: fix detection of HAVE_DECL_SMPI_PROCESS_SET_USER_DATA

mpi/src/mpi/starpu_mpi_mpi.c

@@ -102,7 +102,7 @@ extern struct _starpu_mpi_req *_starpu_mpi_irecv_common(starpu_data_handle_t dat
 extern int smpi_simulated_main_(int argc, char *argv[]);
 
 #pragma weak smpi_process_set_user_data
-#if !HAVE_DECL_SMPI_PROCESS_SET_USER_DATA
+#if !defined(HAVE_DECL_SMPI_PROCESS_SET_USER_DATA)
 extern void smpi_process_set_user_data(void *);
 #endif