Requirements: add CctoolsRequirement

Install it as a dependency unless already satisfied by Xcode.

require cctools_requirement

cctools_requirement should be satisfied by cctools present in opt

add build_env => false to the satify block options in CctoolsRequirement

Library/Homebrew/cmd/install.rb

@@ -122,13 +122,13 @@ module Homebrew
   end
 
   def check_xcode
-    # TODO: reinstate check_for_bad_install_name_tool
+    # TODO: reinstate check_for_bad_install_name_tool and check_for_installed_developer_tools
     # currently check_for_bad_install_name_tool fails because it tries to call
     # the /usr/bin/otool stub program on systems without XCode/CLT
+    # check_for_installed_developer_tools doesn't fail, but produces a warning
+    # when one is no longer required
     checks = Checks.new
     %w[
-      check_for_unsupported_osx
-      check_for_installed_developer_tools
       check_xcode_license_approved
       check_for_osx_gcc_installer
     ].each do |check|

Library/Homebrew/formula_installer.rb

@@ -13,6 +13,7 @@ require "cmd/postinstall"
 require "hooks/bottles"
 require "debrew"
 require "sandbox"
+require "requirements/cctools_requirement"
 
 class FormulaInstaller
   include FormulaCellarChecks
@@ -328,8 +329,10 @@ class FormulaInstaller
   end
 
   def install_relocation_tools
-    ohai "placeholder"
+    cctools = CctoolsRequirement.new
-    true
+    return if cctools.satisfied?
+
+    install_dependency(cctools.to_dependency, inherited_options_for(cctools))
   end
 
   class DependencyInstaller < FormulaInstaller

Library/Homebrew/requirements/cctools_requirement.rb

@@ -2,7 +2,7 @@ class CctoolsRequirement < Requirement
   fatal true
   default_formula 'cctools'
 
-  satisfy do
+  satisfy(:build_env => false) do
-    MacOS::XCode.installed? || MacOS::CLT.installed?
+    MacOS::Xcode.installed? || MacOS::CLT.installed? || Formula['cctools'].installed?
   end
 end