This method is currently unused and after inspecting the git history, it
appears it may never have been used at all.

Instead we use which with a custom PATH.

We override ENV[] to always return strings under superenv, because
legacy formulae assume that CFLAGS, etc. are non-nil.

However, the current implementation has a bug. If I simply concatenate
ENV['CFLAGS'] with another string, it mutates ENV['CFLAGS']:

  irb> ENV['CFLAGS']
  => ""
  irb> ENV['CFLAGS'] + 'a'
  => "a"
  irb> ENV['CFLAGS']
  => "a"

Instead, let's simply return an empty string if the key doesn't exist.
This is sufficient because the following are equivalent:

  1. ENV['CFLAGS'] += "string"
  2. ENV['CFLAGS'] = ENV['CFLAGS'] + "string"

We want to be able to extend this module onto an arbitrary hash and use
it without mutating ENV, for testing purposes.

As discussed in https://github.com/mxcl/homebrew/pull/21936



Closes Homebrew/homebrew#21942.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Closes Homebrew/homebrew#21733.
Closes Homebrew/homebrew#21782.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Fixes Homebrew/homebrew#21943.

This defines the new HOMEBREW_ARCHS environment variable, which is
currently only set during universal builds, so that the tool wrappers
no longer need to hardcode i386/x86_64.

Also adds some reusable constants into the global Hardware::CPU
namespace, available on both OS X and Linux.

Replaced the plethora of ternaries we've used all over the place to
determine whether x86_64 or i386 is called for.

This replaces hardcoding of i386/x86_64 all over the code.