Guess Xcode version if xcodebuild doesn't exist

Library/Homebrew/utils.rb

@@ -297,8 +297,30 @@ module MacOS extend self
 
   def xcode_version
     @xcode_version ||= begin
+      raise unless system "/usr/bin/which -s xcodebuild"
       `xcodebuild -version 2>&1` =~ /Xcode (\d(\.\d)*)/
       $1
+    rescue
+      # for people who don't have xcodebuild installed due to using
+      # some variety of minimal installer, let's try and guess their
+      # Xcode version
+      case llvm_build_version.to_i
+      when 0..2063 then "3.1.0"
+      when 2064..2065 then "3.1.4"
+      when 2366..2325
+        # we have no data for this range so we are guessing
+        "3.2.0"
+      when 2326
+        # also applies to "3.2.3"
+        "3.2.4"
+      when 2327..2333 then "3.2.5"
+      when 2335
+        # this build number applies to 3.2.6, 4.0 and 4.1
+        # https://github.com/mxcl/homebrew/wiki/Xcode
+        "4.0"
+      else
+        "4.2"
+      end
     end
   end