flake: update newNixpkgs for newer prometheus-cpp

flake.lock

@@ -18,17 +18,17 @@
     },
     "newNixpkgs": {
       "locked": {
-        "lastModified": 1646588256,
-        "narHash": "sha256-ZHljmNlt19nSm0Mz8fx6QEhddKUkU4hhwFmfNmGn+EY=",
+        "lastModified": 1647023429,
+        "narHash": "sha256-LdMTXEgW+G1LXrGrME1b1CpTC6/r+meFZDHeXR2Ps40=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "2ebb6c1e5ae402ba35cca5eec58385e5f1adea04",
+        "rev": "9b095223a5dc9a6bce6ec54477f31194871eca8e",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixos-21.11",
         "repo": "nixpkgs",
+        "rev": "9b095223a5dc9a6bce6ec54477f31194871eca8e",
         "type": "github"
       }
     },

flake.nix

@@ -3,7 +3,8 @@
 
   # FIXME: All the pinned versions of nix/nixpkgs have a broken foreman (yes,
   # even 2.7.0's Nixpkgs pin).
-  inputs.newNixpkgs.url = "github:NixOS/nixpkgs/nixos-21.11";
+  # FIXME: has updated prometheus-cpp: https://github.com/NixOS/nixpkgs/pull/163695
+  inputs.newNixpkgs.url = "github:NixOS/nixpkgs/9b095223a5dc9a6bce6ec54477f31194871eca8e";
   inputs.nixpkgs.follows = "nix/nixpkgs";
   inputs.nix.url = github:NixOS/nix/2.6.0;
 
@@ -41,6 +42,12 @@
       # A Nixpkgs overlay that provides a 'hydra' package.
       overlay = final: prev: {
 
+        # Overlay these packages to use dependencies from the Nixpkgs everything
+        # else uses, to side-step the version difference: glibc is 2.32 in the
+        # nix-pinned Nixpkgs, but 2.33 in the newNixpkgs commit.
+        civetweb = final.callPackage "${newNixpkgs}/pkgs/development/libraries/civetweb" { };
+        prometheus-cpp = final.callPackage "${newNixpkgs}/pkgs/development/libraries/prometheus-cpp" { };
+
         # Add LDAP dependencies that aren't currently found within nixpkgs.
         perlPackages = prev.perlPackages // {
           TestPostgreSQL = final.perlPackages.buildPerlModule {