adds configure-time check for the MPI reduce problem

config/checkdoc/test_mpi_reduce_unsigned.txt

+
+Your MPI library does not correctly perform the reduce operations for unsigned
+integers (see https://github.com/pmodels/mpich/issues/6083). It is strongly
+recommended to switch to a version of MPI that is not affected with the issue.
+
+Alternatively, you can disable this test with the configure argument
+"--disable-mpi-checks" but this might result into a non-working YAC build.

config/checksrc/test_mpi_reduce_unsigned.c

 #include <stdlib.h>
 #include <stdio.h>
 #include <limits.h>
+#include <inttypes.h>
 
 #include <mpi.h>
 
+// acx_mpi_job_count=2
+
 int main(int argc, char **argv) {
 
   // init mpi
@@ -29,7 +32,7 @@ int main(int argc, char **argv) {
       if ((recv_data[0] != 0) || (recv_data[1] != 0)) {
         fprintf(
           stderr, "ERROR in MPI_Reduce (MPI_UNSIGNED_LONG): "
-          "recv_data = [%zu; %zu] (expected [0,0])\n",
+          "recv_data = [%lu; %lu] (expected [0,0])\n",
           recv_data[0], recv_data[1]);
         MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
       }
@@ -43,7 +46,7 @@ int main(int argc, char **argv) {
       if ((recv_data[0] != 0) || (recv_data[1] != 0)) {
         fprintf(
           stderr, "ERROR in MPI_Reduce (MPI_UINT8_T): "
-          "recv_data = [%zu; %zu] (expected [0,0])\n",
+          "recv_data = [%"PRIu8"; %"PRIu8"] (expected [0,0])\n",
           recv_data[0], recv_data[1]);
         MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
       }
@@ -57,7 +60,7 @@ int main(int argc, char **argv) {
       if ((recv_data[0] != 0) || (recv_data[1] != 0)) {
         fprintf(
           stderr, "ERROR in MPI_Reduce (MPI_UINT32_T): "
-          "recv_data = [%zu; %zu] (expected [0,0])\n",
+          "recv_data = [%"PRIu32"; %"PRIu32"] (expected [0,0])\n",
           recv_data[0], recv_data[1]);
         MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
       }
@@ -71,7 +74,7 @@ int main(int argc, char **argv) {
       if ((recv_data[0] != 0) || (recv_data[1] != 0)) {
         fprintf(
           stderr, "ERROR in MPI_Reduce (MPI_UINT64_T): "
-          "recv_data = [%zu; %zu] (expected [0,0])\n",
+          "recv_data = [%"PRIu64"; %"PRIu64"] (expected [0,0])\n",
           recv_data[0], recv_data[1]);
         MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
       }