FormulaInstaller: add prevent_build_flags to eliminate code repetition

remove unneeded definition

change variable in FormulaInstaller.check_build_flags from bf to build_flags

Library/Homebrew/cmd/install.rb

@@ -40,11 +40,7 @@ module Homebrew
 
       # if the user's flags will prevent bottle only-installations when no
       # developer tools are available, we need to stop them early on
-      if !MacOS.can_build?
-        bf = ARGV.collect_build_flags
-
-        raise BuildFlagsError.new(bf) if !bf.empty?
-      end
+      FormulaInstaller.prevent_build_flags unless MacOS.can_build?
 
       ARGV.formulae.each do |f|
         # head-only without --HEAD is an error

Library/Homebrew/cmd/reinstall.rb

@@ -2,13 +2,7 @@ require "formula_installer"
 
 module Homebrew
   def reinstall
-    if !MacOS.can_build?
-      bf = ARGV.collect_build_flags
-
-      if !bf.empty?
-        raise BuildFlagsError.new(bf)
-      end
-    end
+    FormulaInstaller.prevent_build_flags unless MacOS.can_build?
 
     ARGV.resolved_formulae.each { |f| reinstall_formula(f) }
   end

Library/Homebrew/cmd/upgrade.rb

@@ -3,13 +3,7 @@ require "cmd/outdated"
 
 module Homebrew
   def upgrade
-    if !MacOS.can_build?
-      bf = ARGV.collect_build_flags
-
-      if !bf.empty?
-        raise BuildFlagsError.new(bf)
-      end
-    end
+    FormulaInstaller.prevent_build_flags unless MacOS.can_build?
 
     Homebrew.perform_preinstall_checks
 

Library/Homebrew/formula_installer.rb

@@ -56,6 +56,13 @@ class FormulaInstaller
     @pour_failed   = false
   end
 
+  # called by install/reinstall/upgrade when no build tools are available
+  def self.prevent_build_flags
+    build_flags = ARGV.collect_build_flags
+
+    raise BuildFlagsError.new(build_flags) unless build_flags.empty?
+  end
+
   def pour_bottle?(install_bottle_options = { :warn=>false })
     return true if Homebrew::Hooks::Bottles.formula_has_bottle?(formula)
 
@@ -234,8 +241,6 @@ class FormulaInstaller
   end
 
   def check_dependencies_bottled(deps)
-    unbottled = []
-
     unbottled = deps.select do |dep, _|
       formula = dep.to_formula
       !formula.pour_bottle? && !MacOS.can_build?