Fix GPI-2 and enable TAGASPI

The rdma-core driver.h include is no longer installed:

 56dd87acd2

So ibv_read_sysfs_file() is not defined. As the symbols is still
distributed, we simply add the missing prototype manually.

Similarly, the gaspi_size_t gaspi_get_system_mem() function is not
available from the gaspi public headers, so we define it in the
max_mem.c test.

Fixes: rarias/bscpkgs#7

flake.nix

@@ -3,36 +3,15 @@
 
   outputs = { self, nixpkgs, ...}:
   let
-    system = "x86_64-linux";
     pkgs = import nixpkgs {
-      inherit system;
       # For now we only support x86
+      system = "x86_64-linux";
       overlays = [ self.overlays.default ];
     };
   in
     {
       bscOverlay = import ./overlay.nix;
       overlays.default = self.bscOverlay;
-
-      # propagate nixpkgs lib, so we can do bscpkgs.lib
-      inherit (nixpkgs) lib;
-
-      # full nixpkgs with our overlay applied
-      legacyPackages.${system} = pkgs;
-
-      # packages added by our overlay
-      packages.${system} =
-        let
-          inherit (builtins) attrNames removeAttrs;
-          inherit (nixpkgs.lib) flip filterAttrs getAttrs pipe isDerivation;
-        in
-          # extract the names of the packages from the overlay, then get the
-          # actual packages from the full package set with the overlay applied
-          pipe (self.overlays.default null { inherit (nixpkgs) lib; } ) [
-            attrNames
-            (flip getAttrs pkgs)
-            (flip removeAttrs [ "bsc" ])
-            (filterAttrs (_: isDerivation))
-          ];
+      legacyPackages.x86_64-linux = pkgs;
     };
 }