CityHash on MacOS X with ruby 1.9.2 from rvm

gistfile1.txt

>> require 'cityhash'
LoadError: Could not open library '/Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/cityhash-0.4.0/lib/cityhash/ext/libcity.so': dlopen(/Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/cityhash-0.4.0/lib/cityhash/ext/libcity.so, 5): no suitable image found.  Did find:
	/Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/cityhash-0.4.0/lib/cityhash/ext/libcity.so: unknown file type, first eight bytes: 0x7F 0x45 0x4C 0x46 0x01 0x01 0x01 0x00
	from /Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/ffi-1.0.7/lib/ffi/library.rb:75:in `block in ffi_lib'
	from /Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/ffi-1.0.7/lib/ffi/library.rb:54:in `map'
	from /Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/ffi-1.0.7/lib/ffi/library.rb:54:in `ffi_lib'
	from /Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/cityhash-0.4.0/lib/cityhash.rb:11:in `<module:Internal>'
	from /Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/cityhash-0.4.0/lib/cityhash.rb:8:in `<module:CityHash>'
	from /Users/pepe/.rvm/gems/ruby-1.9.2-p180/gems/cityhash-0.4.0/lib/cityhash.rb:3:in `<top (required)>'
	from <internal:lib/rubygems/custom_require>:33:in `require'
	from <internal:lib/rubygems/custom_require>:33:in `rescue in require'
	from <internal:lib/rubygems/custom_require>:29:in `require'
	from (irb):1
	from /Users/pepe/.rvm/rubies/ruby-1.9.2-p180/bin/irb:16:in `<main>'

I had the same problem. There is a bug in the C code where ssize_t is appears instead of size_t
This is why it does not compile