Add a nix shell with glibc 2.26

nix/shell-glibc-2.26.nix

@@ -0,0 +1,45 @@
+{
+  pkgs ? import (
+    builtins.fetchTarball {
+      # Use nixpkgs 18.03 with old glibc and cmake
+      url = "https://github.com/NixOS/nixpkgs/archive/3e1be2206b4c1eb3299fb633b8ce9f5ac1c32898.tar.gz";
+    }
+  ) {}
+
+# By default use debug
+, enableDebug ? true
+}:
+
+with pkgs;
+
+{ 
+  ovni = stdenv.mkDerivation rec {
+    name = "ovni";
+
+    buildInputs = [ cmake openmpi ];
+
+    cmakeBuildType = if (enableDebug) then "Debug" else "Release";
+    dontStrip = true;
+
+    src = ../.;
+  };
+
+  shell = pkgs.mkShell {
+    nativeBuildInputs = [ cmake openmpi ];
+    NIX_ENFORCE_PURITY = 0;
+    shellHook = ''
+      set -e
+      curdir=$(pwd)
+      rm -rf build install
+      mkdir build install
+      cd build
+      cmake -DCMAKE_BUILD_TYPE=Debug \
+        -DENABLE_DEBUG_LOG=ON \
+        -DCMAKE_INSTALL_PREFIX="$curdir/install" ..
+      make VERBOSE=1
+      make test
+      make install
+      exit 0
+    '';
+  };
+}