packaging: build recipes for arch, gentoo, nix, void, fedora

Five distro recipes in packaging/, all following the same recipe:
unpack the Gitea release archive (which extracts to fastwc/), run
autoreconf -fi (the generated configure/Makefile.in are not committed),
configure, make, make install - the binary needs only glibc.

Each recipe notes the release prerequisite: the archive URL requires a
v0.1.0 tag on the remote, and Arch/Nix/Void carry an integrity
placeholder to fill in once the tag exists. The PKGBUILD was validated
with makepkg --printsrcinfo, and the full build recipe was run
end-to-end from a Gitea-layout tarball (autoreconf, configure, make,
make install DESTDIR) producing a working /usr/bin/fastwc.

packaging/nix/default.nix

@@ -0,0 +1,29 @@
+{ lib, stdenv, fetchFromGitea, autoconf, automake, libtool }:
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "fastwc";
+  version = "0.1.0";
+
+  src = fetchFromGitea {
+    domain = "git.spectoria.dev";
+    owner = "huntedbytheirs";
+    repo = "fastwc";
+    # requires a v0.1.0 tag on the Gitea remote; the fake hash makes the
+    # first build fail with the real one printed - drop it in, then rebuild
+    rev = "v${finalAttrs.version}";
+    hash = lib.fakeHash;
+  };
+
+  nativeBuildInputs = [ autoconf automake libtool ];
+
+  preConfigure = ''
+    autoreconf -fi
+  '';
+
+  meta = with lib; {
+    description = "A wc replacement that beats GNU wc - SIMD kernels, mmap, threads";
+    homepage = "https://git.spectoria.dev/huntedbytheirs/fastwc";
+    license = licenses.mit;
+    platforms = platforms.linux;
+  };
+})