Add nix flake config

flake.nix

@@ -0,0 +1,53 @@
+{
+  description = "Flake for Clice";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }: 
+    flake-utils.lib.eachDefaultSystem 
+      (system: 
+        let 
+          pkgs = nixpkgs.legacyPackages.${system}; 
+          tomlplusplus = pkgs.tomlplusplus.overrideAttrs (oldAttrs: {
+            postInstall = oldAttrs.postInstall or "" + ''
+              ln -s $out/lib/libtomlplusplus.so $out/lib/libtoml++.so              
+            '';
+          });
+        in {
+          devShell = pkgs.mkShell {
+            buildInputs = [
+              pkgs.gcc
+              pkgs.pkg-config
+              pkgs.xmake
+              pkgs.cmake
+              pkgs.ninja
+              pkgs.python3
+              pkgs.gtest
+              pkgs.libuv
+              pkgs.llvmPackages_20.libstdcxxClang
+              pkgs.llvmPackages_20.libllvm
+              pkgs.llvmPackages_20.bintools
+              pkgs.llvmPackages_20.compiler-rt
+              pkgs.llvmPackages_20.libunwind
+
+              tomlplusplus
+            ];
+
+            shellHook = 
+              let 
+                gcc = pkgs.gcc-unwrapped;
+                gccInclude = "${gcc}/include";
+                gccCxxIncludePath = "${gccInclude}/c++/${gcc.lib.version}";
+              in 
+              ''
+                export NIX_CFLAGS_COMPILE+=" -isystem ${gccInclude}"
+                export NIX_CFLAGS_COMPILE+=" -isystem ${gccCxxIncludePath}"
+                export NIX_CFLAGS_COMPILE+=" -isystem ${gccCxxIncludePath}/$(gcc -dumpmachine)"
+              '';
+          };
+        }
+      );
+}