Pass the ENV hash into the BuildError constructor

Library/Homebrew/exceptions.rb

@@ -147,9 +147,9 @@ end
 class BuildError < Homebrew::InstallationError
   attr_reader :command, :env
 
-  def initialize formula, cmd, args
+  def initialize(formula, cmd, args, env)
     @command = cmd
-    @env = ENV.to_hash
+    @env = env
     args = args.map{ |arg| arg.to_s.gsub " ", "\\ " }.join(" ")
     super formula, "Failed executing: #{command} #{args}"
   end

Library/Homebrew/formula.rb

@@ -545,7 +545,7 @@ class Formula
         log.puts
         require 'cmd/config'
         Homebrew.dump_build_config(log)
-        raise BuildError.new(self, cmd, args)
+        raise BuildError.new(self, cmd, args, ENV.to_hash)
       end
     ensure
       log.close unless log.closed?