collectd: fix build and modernize derivation slightly

1. I experienced intermittent connection failures to <https://collectd.org> and I suspect it's hosted on hobbyist equipment.
This made the `src` derivation flaky, so I switched to the upstream GitHub repository.
It seems better to use the actual source instead of a prepared tarball from the release process anyway.

2. When building out of the source instead of the release tarball, we need to run Bison and Flex to generate the parser and lexer, and we need Perl for `pod2man`.

3. As the [build error on Hydra](https://hydra.nixos.org/build/300269816) notes, `src/virt.c` makes use of some token `ATTRIBUTE_UNUSED` but it's not defined anywhere. Define it.

4. Switch all hashes to use the SRI style.

5. Switch to `finalAttrs` fixpoint style for better overriding.

6. Reduce the scope of `with lib;` in the `meta` section.

Bit of a smörgåsbord but not too bad.

pkgs/tools/system/collectd/default.nix

···
 {
   lib,
   stdenv,
-  fetchurl,
+  fetchFromGitHub,
   fetchpatch,
   callPackage,
   autoreconfHook,
   pkg-config,
   libtool,
+  bison,
+  flex,
+  perl,
   nixosTests,
   ...
 }@args:
 let
   plugins = callPackage ./plugins.nix args;
 in
-stdenv.mkDerivation rec {
+stdenv.mkDerivation (finalAttrs: {
+  pname = "collectd";
   version = "5.12.0";
-  pname = "collectd";
 
-  src = fetchurl {
-    url = "https://collectd.org/files/${pname}-${version}.tar.bz2";
-    sha256 = "1mh97afgq6qgmpvpr84zngh58m0sl1b4wimqgvvk376188q09bjv";
+  src = fetchFromGitHub {
+    owner = "collectd";
+    repo = "collectd";
+    tag = "collectd-${finalAttrs.version}";
+    hash = "sha256-UTlCY1GPRpbdQFLFUDjNr1PgEdGv4WNtjr8TYbxHK5A=";
   };
 
+  # All of these are going to be included in the next release
   patches = [
     # fix -t never printing syntax errors
     # should be included in next release
     (fetchpatch {
+      name = "fix-broken-dash-t-option.patch";
       url = "https://github.com/collectd/collectd/commit/3f575419e7ccb37a3b10ecc82adb2e83ff2826e1.patch";
-      sha256 = "0jwjdlfl0dp7mlbwygp6h0rsbaqfbgfm5z07lr5l26z6hhng2h2y";
+      hash = "sha256-XkDxLITmG0FLpgf8Ut1bDqulM4DmPs8Xrec2QB1tkks=";
     })
     (fetchpatch {
       name = "no_include_longintrepr.patch";
···
   nativeBuildInputs = [
     pkg-config
     autoreconfHook
+    bison
+    flex
+    perl # for pod2man
   ];
+
   buildInputs = [
     libtool
   ] ++ plugins.buildInputs;
···
     ++ plugins.configureFlags
     ++ lib.optionals (stdenv.buildPlatform != stdenv.hostPlatform) [ "--with-fp-layout=nothing" ];
 
+  # Used in `src/virt.c`
+  env.NIX_CFLAGS_COMPILE = "-DATTRIBUTE_UNUSED=__attribute__((unused))";
+
   # do not create directories in /var during installPhase
   postConfigure = ''
-    substituteInPlace Makefile --replace '$(mkinstalldirs) $(DESTDIR)$(localstatedir)/' '#'
+    substituteInPlace Makefile --replace-fail '$(mkinstalldirs) $(DESTDIR)$(localstatedir)/' '#'
   '';
 
   postInstall = ''
···
     inherit (nixosTests) collectd;
   };
 
-  meta = with lib; {
+  meta = {
     description = "Daemon which collects system performance statistics periodically";
     homepage = "https://collectd.org";
-    license = licenses.gpl2Plus;
-    platforms = platforms.unix;
-    maintainers = with maintainers; [ bjornfor ];
+    license = lib.licenses.gpl2Plus;
+    platforms = lib.platforms.unix;
+    maintainers = with lib.maintainers; [ bjornfor ];
   };
-}
+})