add HOMEBREW_ENV_PATH internal variable

`Library/ENV` like `Library/Homebrew` is part of Homebrew basecode. It
should be able to be accessed during the `brew tests`.

By adding HOMEBREW_ENV_PATH variable, we allow test suit to locate these
codes.

Library/Homebrew/config.rb

@@ -39,6 +39,7 @@ HOMEBREW_PREFIX = Pathname.new(ENV["HOMEBREW_PREFIX"])
 HOMEBREW_REPOSITORY = Pathname.new(ENV["HOMEBREW_REPOSITORY"])
 
 HOMEBREW_LIBRARY = Pathname.new(ENV["HOMEBREW_LIBRARY"])
+HOMEBREW_ENV_PATH = HOMEBREW_LIBRARY/"ENV"
 HOMEBREW_CONTRIB = HOMEBREW_REPOSITORY/"Library/Contributions"
 
 # Where we store built products

Library/Homebrew/extend/ENV/std.rb

@@ -77,7 +77,7 @@ module Stdenv
     paths = []
     paths << "#{HOMEBREW_PREFIX}/lib/pkgconfig"
     paths << "#{HOMEBREW_PREFIX}/share/pkgconfig"
-    paths << "#{HOMEBREW_LIBRARY}/ENV/pkgconfig/#{MacOS.version}"
+    paths << "#{HOMEBREW_ENV_PATH}/pkgconfig/#{MacOS.version}"
     paths << "/usr/lib/pkgconfig"
     paths.select { |d| File.directory? d }.join(File::PATH_SEPARATOR)
   end

Library/Homebrew/extend/ENV/super.rb

@@ -28,7 +28,7 @@ module Superenv
   def self.bin
     return unless MacOS.has_apple_developer_tools?
 
-    bin = (HOMEBREW_REPOSITORY/"Library/ENV").subdirs.reject { |d| d.basename.to_s > MacOS::Xcode.version }.max
+    bin = HOMEBREW_ENV_PATH.subdirs.reject { |d| d.basename.to_s > MacOS::Xcode.version }.max
     bin.realpath unless bin.nil?
   end
 
@@ -150,7 +150,7 @@ module Superenv
   end
 
   def determine_pkg_config_libdir
-    paths = %W[/usr/lib/pkgconfig #{HOMEBREW_LIBRARY}/ENV/pkgconfig/#{MacOS.version}]
+    paths = %W[/usr/lib/pkgconfig #{HOMEBREW_ENV_PATH}/pkgconfig/#{MacOS.version}]
     paths << "#{MacOS::X11.lib}/pkgconfig" << "#{MacOS::X11.share}/pkgconfig" if x11?
     paths.to_path_s
   end

Library/Homebrew/test/lib/config.rb

@@ -14,6 +14,7 @@ HOMEBREW_PREFIX        = Pathname.new(TEST_TMPDIR).join("prefix")
 HOMEBREW_REPOSITORY    = HOMEBREW_PREFIX
 HOMEBREW_LIBRARY       = HOMEBREW_REPOSITORY+"Library"
 HOMEBREW_LIBRARY_PATH  = Pathname.new(File.expand_path("../../..", __FILE__))
+HOMEBREW_ENV_PATH      = HOMEBREW_LIBRARY_PATH.parent+"ENV"
 HOMEBREW_LOAD_PATH     = [File.expand_path("..", __FILE__), HOMEBREW_LIBRARY_PATH].join(":")
 HOMEBREW_CACHE         = HOMEBREW_PREFIX.parent+"cache"
 HOMEBREW_CACHE_FORMULA = HOMEBREW_PREFIX.parent+"formula_cache"

Library/Homebrew/test/testing_env.rb

@@ -6,7 +6,7 @@ require "global"
 require "formulary"
 
 # Test environment setup
-%w[ENV Formula].each { |d| HOMEBREW_LIBRARY.join(d).mkpath }
+HOMEBREW_LIBRARY.join("Formula").mkpath
 %w[cache formula_cache cellar logs].each { |d| HOMEBREW_PREFIX.parent.join(d).mkpath }
 
 # Test fixtures and files can be found relative to this path

Library/brew.rb

@@ -50,7 +50,7 @@ begin
   end
 
   # Add SCM wrappers.
-  ENV["PATH"] += "#{File::PATH_SEPARATOR}#{HOMEBREW_LIBRARY}/ENV/scm"
+  ENV["PATH"] += "#{File::PATH_SEPARATOR}#{HOMEBREW_ENV_PATH}/scm"
 
   if cmd
     internal_cmd = require? HOMEBREW_LIBRARY_PATH.join("cmd", cmd)