Merge outputs of MPI in a single directory

Some MPI implementations now have their headers in the dev output as
well as the mpicc wrappers.

Reviewed-by: Aleix Boné <abonerib@bsc.es>

pkgs/tagaspi/default.nix

@@ -11,8 +11,16 @@
 , numactl
 , rdma-core
 , gfortran
+, symlinkJoin
 }:
 
+let
+  mpiAll = symlinkJoin {
+    name = "mpi-all";
+    paths = [ mpi.all ];
+  };
+in
+
 stdenv.mkDerivation rec {
   pname = "tagaspi";
   enableParallelBuilding = true;
@@ -32,10 +40,10 @@ stdenv.mkDerivation rec {
     autoconf
     libtool
     boost
-    mpi
     numactl
     rdma-core
     gfortran
+    mpiAll
   ];
 
   dontDisableStatic = true;