Prevent ffi and childprocess causing build failures (#2595)

Author: JonRowe

Gemfile

@@ -34,6 +34,8 @@ end
 
 if RUBY_VERSION < '2.2.0' && !!(RbConfig::CONFIG['host_os'] =~ /cygwin|mswin|mingw|bccwin|wince|emx/)
   gem 'ffi', '< 1.10'
+elsif RUBY_VERSION < '2.0.0' && !!(RbConfig::CONFIG['host_os'] =~ /cygwin|mswin|mingw|bccwin|wince|emx/)
+  gem 'ffi', '< 1.9.15' # allow ffi to be installed on older rubies on windows
 elsif RUBY_VERSION < '1.9'
   gem 'ffi', '< 1.9.19' # ffi dropped Ruby 1.8 support in 1.9.19
 else