freebsd.libutil: add option to build with pwd_mkdb path

pkgs/os-specific/bsd/freebsd/pkgs/libpam.nix

@@ -2,6 +2,8 @@
   mkDerivation,
   openssl,
   libradius,
+  libutil,
+  pwd_mkdb,
 }:
 mkDerivation {
   path = "lib/libpam/libpam";
@@ -15,6 +17,9 @@ mkDerivation {
   buildInputs = [
     libradius
     openssl
+    (libutil.override {
+      withPwdMkdb = pwd_mkdb;
+    })
   ];
 
   MK_NIS = "no"; # TODO

pkgs/os-specific/bsd/freebsd/pkgs/libutil.nix

@@ -1,9 +1,11 @@
 {
+  lib,
   mkDerivation,
   include,
   libgcc,
   libcMinimal,
   csu,
+  withPwdMkdb ? null,
 }:
 mkDerivation {
   path = "lib/libutil";
@@ -26,6 +28,11 @@ mkDerivation {
     libcMinimal
   ];
 
+  # XXX mass rebuild moment
+  postPatch = if withPwdMkdb == null then null else ''
+    substituteInPlace lib/libutil/pw_util.c --replace-fail _PATH_PWD_MKDB '"${lib.getExe withPwdMkdb}"'
+  '';
+
   preBuild = ''
     export NIX_CFLAGS_COMPILE="$NIX_CFLAGS_COMPILE -B${csu}/lib"
   '';

pkgs/os-specific/bsd/freebsd/pkgs/pwd_mkdb.nix

@@ -3,4 +3,6 @@ mkDerivation {
   path = "usr.sbin/pwd_mkdb";
 
   extraPaths = [ "lib/libc/gen" ];
+
+  meta.mainProgram = "pwd_mkdb";
 }