mpi/tests/sendrecv_gemm_bench.c: disable test when running MPI backend

mpi/tests/sendrecv_gemm_bench.c

@@ -320,7 +320,13 @@ static void* comm_thread_func(void* arg)
 	return NULL;
 }
 
-
+#ifdef STARPU_USE_MPI_MPI
+int main(int argc, char **argv)
+{
+	FPRINTF(stderr, "This test does not work with the MPI backend.\n");
+	return STARPU_TEST_SKIPPED;
+}
+#else
 int main(int argc, char **argv)
 {
 	double start, end;
@@ -461,3 +467,4 @@ enodev:
 
 	return ret;
 }
+#endif