test: add sigsegv after MPI_Finalize test

The current srun version used in MN4 returns 0 if the program crashes
after MPI_Finalize, as shown by this test.

overlay.nix

@@ -214,9 +214,10 @@ let
       inherit self super bsc callPackage;
     };
 
-#    test = {
+    test = {
 #      hwloc = callPackage ./test/bugs/hwloc.nix { };
-#    };
+      sigsegv = callPackage ./test/reproducers/sigsegv.nix { };
+    };
   });
 
 in

test/reproducers/sigsegv.c

@@ -0,0 +1,35 @@
+#include <mpi.h>
+#include <stdio.h>
+#include <signal.h>
+#include <stdlib.h>
+
+void sigsegv(int rank)
+{
+        if (rank == 2) raise(SIGSEGV);
+}
+
+int main(int argc, char *argv[])
+{
+        int rank;
+        char where;
+
+        MPI_Init(&argc, &argv);
+
+        if(!argv[1])
+        {
+                fprintf(stderr, "missing \"before\" or \"after\" argument\n");
+                exit(1);
+        }
+
+        MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+        where = argv[1][0];
+
+        if(where == 'b') sigsegv(rank);
+
+        MPI_Finalize();
+
+        if(where == 'a') sigsegv(rank);
+
+        return 0;
+}

test/reproducers/sigsegv.nix

@@ -0,0 +1,20 @@
+{
+  stdenv
+, mpi
+}:
+
+stdenv.mkDerivation {
+  name = "sigsegv";
+
+  src = ./.;
+
+  buildInputs = [ mpi ];
+
+  buildPhase = ''
+    mpicc sigsegv.c -o sigsegv
+  '';
+
+  installPhase = ''
+    cp sigsegv $out
+  '';
+}