util-linux: make dependencies on pam and libcap optional

Introduce new boolean arguments "pamSupport" and "capabilitiesSupport" that
control whether "pam" and "libcap" are compiled in. These flags are true by
default, so this commit does not cause any rebuilds.

pkgs/os-specific/linux/util-linux/default.nix

@@ -1,6 +1,10 @@
-{ lib, stdenv, fetchurl, pkg-config, zlib, shadow, libcap_ng
+{ lib, stdenv, fetchurl, pkg-config, zlib, shadow
+, capabilitiesSupport ? true
+, libcap_ng
 , ncursesSupport ? true
-, ncurses, pam
+, ncurses
+, pamSupport ? true
+, pam
 , systemdSupport ? stdenv.isLinux && !stdenv.hostPlatform.isStatic
 , systemd
 , nlsSupport ? true
@@ -59,7 +63,9 @@ stdenv.mkDerivation rec {
   ];
 
   nativeBuildInputs = [ pkg-config ];
-  buildInputs = [ zlib pam libcap_ng ]
+  buildInputs = [ zlib ]
+    ++ lib.optionals pamSupport [ pam ]
+    ++ lib.optionals capabilitiesSupport [ libcap_ng ]
     ++ lib.optionals ncursesSupport [ ncurses ]
     ++ lib.optionals systemdSupport [ systemd ];