Fix osu cross-compilation

pkgs/gpi-2/default.nix

@@ -43,7 +43,7 @@ stdenv.mkDerivation rec {
 
   configureFlags = [
     "--with-infiniband=${rdma-core-all}"
-    "--with-mpi=yes"
+    "--with-mpi=yes" # fixes mpi detection when cross-compiling
     "--with-slurm"
     "CFLAGS=-fPIC"
     "CXXFLAGS=-fPIC"
@@ -70,6 +70,6 @@ stdenv.mkDerivation rec {
     maintainers = with lib.maintainers.bsc; [ rarias ];
     platforms = lib.platforms.linux;
     license = lib.licenses.gpl3Plus;
-    cross = false;
+    cross = false; # infiniband detection does not work
   };
 }