libsodium: use pkg-config

use pkg-config to force .pc

Closes Homebrew/homebrew#30681

Closes Homebrew/homebrew#30682.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/libsodium.rb

@@ -4,6 +4,7 @@ class Libsodium < Formula
   homepage "https://github.com/jedisct1/libsodium/"
   url "https://github.com/jedisct1/libsodium/releases/download/0.6.0/libsodium-0.6.0.tar.gz"
   sha256 "84cdb6bf8ae3384f3ef78636f93bc689df748c1d36f87d4b6ab1e31c2d4dd145"
+  revision 1
 
   bottle do
     cellar :any
@@ -12,6 +13,8 @@ class Libsodium < Formula
     sha1 "40fcd281e55c4b0925f99f602a95dfc0b6afb6e0" => :lion
   end
 
+  depends_on "pkg-config" => :build
+
   head do
     url "https://github.com/jedisct1/libsodium.git"