Add compatibility layer for `module Homebrew`.

Library/Homebrew/compat.rb

@@ -2,6 +2,7 @@ require "compat/fails_with_llvm"
 require "compat/tap"
 require "compat/formula"
 require "compat/formula_specialties"
+require "compat/global"
 require "compat/hardware"
 require "compat/macos"
 require "compat/md5"

Library/Homebrew/compat/global.rb

+module Homebrew
+  module_function
+
+  def method_missing(method, *args, &block)
+    if instance_methods.include?(method)
+      # odeprecated "#{self}##{method}", "'module_function' or 'def self.#{method}' to convert it to a class method"
+      return instance_method(method).bind(self).call(*args, &block)
+    end
+    super
+  end
+
+  def respond_to_missing?(method, include_private = false)
+    return true if method_defined?(method)
+    super(method, include_private)
+  end
+end