man-only packages: fixup after stdenv changes

Thanks to @avnik for notification.
The stdenv now auto-removes developer-only documentation
unless explicitly indicated, which wasn't a good fit for these packages.

pkgs/data/documentation/man-pages/default.nix

@@ -9,7 +9,10 @@ stdenv.mkDerivation rec {
     sha256 = "0v8zxq4scfixy3pjpw9ankvv5v8frv62khv4xm1jpkswyq6rbqcg";
   };
 
+  # keep developer docs separately (man2 and man3)
+  outputs = [ "out" "docdev" ];
   makeFlags = [ "MANDIR=$(out)/share/man" ];
+  postFixup = ''moveToOutput share/man/man2 "$docdev" '';
 
   meta = with stdenv.lib; {
     inherit version;

pkgs/data/documentation/std-man-pages/default.nix

@@ -2,12 +2,14 @@
 
 stdenv.mkDerivation rec {
   name = "std-man-pages-4.4.0";
-  
+
   src = fetchurl {
     url = mirror://gcc/libstdc++/doxygen/libstdc++-man.4.4.0.tar.bz2;
     sha256 = "0153py77ll759jacq41dp2z2ksr08pdcfic0rwjd6pr84dk89y9v";
   };
 
+  outputDocdev = "out";
+
   installPhase = ''
     mkdir -p $out/share/man
     cp -R * $out/share/man

pkgs/data/documentation/stdman/default.nix

@@ -11,13 +11,15 @@ stdenv.mkDerivation rec {
     sha256 = "09c5gjhcz97ghfrv9zkgfb1wckvmqnhbzga0xidbm1ir7640di8l";
   };
 
+  outputDocdev = "out";
+
   preConfigure = "
     patchShebangs ./configure
     patchShebangs ./do_install
   ";
 
   buildInputs = [ curl ];
-  
+
   meta = with stdenv.lib; {
     description = "Formatted C++11/14 stdlib man pages (cppreference)";
     longDescription = "stdman is a tool that parses archived HTML