brew doctor: update expat check

Apaprently both expat.framework and libexpat.framework exist
and interfere with CMake.

Library/Homebrew/cmd/doctor.rb

@@ -574,9 +574,10 @@ end
 
 def check_for_other_frameworks
   # Other frameworks that are known to cause problems when present
-  if File.exist? "/Library/Frameworks/expat.framework"
+  ["/Library/Frameworks/expat.framework", "/Library/Frameworks/libexpat.framework"].each do |f|
+    if File.exist? f
       puts <<-EOS.undent
-      /Library/Frameworks/expat.framework detected
+        #{f} detected
 
         This will be picked up by Cmake's build system and likey cause the
         build to fail, trying to link to a 32-bit version of expat.
@@ -584,6 +585,7 @@ def check_for_other_frameworks
 
       EOS
     end
+  end
 end
 
 module Homebrew extend self