unrar: Install all C++ header files into the "dev" output

This is e.g. required for the rar2fs build [0], which needs at least
version.hpp, rar.hpp, dllext.hpp, dll.hpp, and headers5.hpp.

At least Gentoo does this as well [1] but most other distributions only
install dll.hpp or no header files at all.

[0]: https://github.com/NixOS/nixpkgs/pull/78189
[1]: https://gitweb.gentoo.org/repo/gentoo.git/tree/app-arch/unrar/unrar-5.8.5.ebuild

pkgs/tools/archivers/unrar/default.nix

@@ -22,6 +22,8 @@ stdenv.mkDerivation rec {
     make lib
   '';
 
+  outputs = [ "out" "dev" ];
+
   installPhase = ''
     install -Dt "$out/bin" unrar
 
@@ -30,7 +32,8 @@ stdenv.mkDerivation rec {
         $out/share/doc/unrar
 
     install -Dm755 libunrar.so $out/lib/libunrar.so
-    install -D dll.hpp $out/include/unrar/dll.hpp
+
+    install -Dt $dev/include/unrar/ *.hpp
   '';
 
   setupHook = ./setup-hook.sh;