Actually cache Xcode.version

The short-circuit returns would cause the caching ||= syntax to be skipped. For me on my CLT-less install, this was noticeably slowing down brew for some operations due to the frequent calls to xcodebuild.

Library/Homebrew/macos/xcode.rb

@@ -56,7 +56,13 @@ module MacOS::Xcode extend self
     # may return a version string
     # that is guessed based on the compiler, so do not
     # use it in order to check if Xcode is installed.
-    @version ||= begin
+    @version ||= uncached_version
+  end
+
+  def uncached_version
+    # This is a separate function as you can't cache the value out of a block
+    # if return is used in the middle, which we do many times in here.
+
     return "0" unless MACOS
 
     # this shortcut makes version work for people who don't realise you
@@ -64,7 +70,7 @@ module MacOS::Xcode extend self
     xcode43build = V4_BUNDLE_PATH/'Contents/Developer/usr/bin/xcodebuild'
     if xcode43build.file?
       `#{xcode43build} -version 2>/dev/null` =~ /Xcode (\d(\.\d)*)/
-        return $1 if $1
+      $1 if $1
     end
 
     # Xcode 4.3 xc* tools hang indefinately if xcode-select path is set thus
@@ -117,7 +123,6 @@ module MacOS::Xcode extend self
       end
     end
   end
-  end
 
   def provides_autotools?
     version.to_f < 4.3