bitlbee-steam: fix build with GCC 15; refactor (#517550)

pkgs/by-name/bi/bitlbee-steam/package.nix

@@ -15,10 +15,10 @@ stdenv.mkDerivation (finalAttrs: {
   pname = "bitlbee-steam";
 
   src = fetchFromGitHub {
-    rev = "v${finalAttrs.version}";
     owner = "bitlbee";
     repo = "bitlbee-steam";
-    sha256 = "121r92mgwv445wwxzh35n19fs5k81ihr0j19k256ia5502b1xxaq";
+    tag = "v${finalAttrs.version}";
+    hash = "sha256-WPUelgClqGiKmClIkGEMaBbtUrBlwN85L4Rs/qpIOYg=";
   };
 
   nativeBuildInputs = [
@@ -37,6 +37,9 @@ stdenv.mkDerivation (finalAttrs: {
     ./autogen.sh
   '';
 
+  # Source uses `bool` as a variable name, reserved in C23.
+  env.NIX_CFLAGS_COMPILE = "-std=gnu17";
+
   meta = {
     description = "Steam protocol plugin for BitlBee";