Won't load as-is on cygwin; very hacky fix included

[apfeltee]

This gem won't be able to be used as-is, since cygwin1.dll apparently does not export the structure of time_t.

Here is a potential fix, assuming LLVM+Clang have been installed into c:/Program Files (x86)/ (default installation path as defined by CMake):

require "ffi"
FFI.add_typedef :pointer, :time_t
FFI.typedef :pointer, :time_t
ENV['LIBCLANG'] = "c:/progra~2/LLVM/bin/libclang.dll"
require "ffi/clang"

Obviously the type definition of time_t here would unusable, but I also have not encountered an issue so far.