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

@@ -13,8 +13,5 @@
       bscOverlay = import ./overlay.nix;
       overlays.default = self.bscOverlay;
       legacyPackages.x86_64-linux = pkgs;
-
-      # propagate nixpkgs lib, so we can do bscpkgs.lib
-      inherit (nixpkgs) lib;
     };
 }

pkgs/llvm-ompss2/clang.nix

@@ -43,22 +43,20 @@ let
 
   source = if (useGit) then git else release;
 
-in stdenv.mkDerivation {
+in stdenv.mkDerivation rec {
   pname = "clang-ompss2";
   inherit (source) src version;
 
   enableParallelBuilding = true;
+  isClang = true;
 
   passthru = {
     CC = "clang";
     CXX = "clang++";
-
-    isClang = true;
-    isClangWithOmpss = true;
-
-    inherit gcc zlib;
   };
 
+  isClangWithOmpss = true;
+
   nativeBuildInputs = [ zlib ];
 
   buildInputs = [