weechat: permit custom perl/ruby usage

CMake doesn't especially care about superenv, so if you have a custom
Ruby or Perl on your system it can pick up the headers from /usr/include
and the libraries from /usr/local/lib for example, which obviously
causes build failures. This handles that situation sanely.

Closes https://github.com/Homebrew/homebrew-core/issues/8372.

Formula/weechat.rb

@@ -28,6 +28,8 @@ class Weechat < Formula
   depends_on "aspell" => :optional
   depends_on "lua" => :optional
   depends_on :python => :optional
+  depends_on :ruby => ["1.8", :optional]
+  depends_on :perl => ["5.3", :optional]
   depends_on "curl" => :optional
 
   def install