`RUBY_PLATFORM` may not contain `mswin` or `mingw`; Add `msys`
MODIFY
mrbgems/mruby-io/mrbgem.rake
mrbgems/mruby-io/mrbgem.rake
@@ -6,7 +6,7 @@ MRuby::Gem::Specification.new('mruby-io') do |spec|
spec.cc.include_paths << "#{build.root}/src"
case RUBY_PLATFORM
- when /mingw|mswin/
+ when /mingw|mswin|msys/
spec.linker.libraries += ['Ws2_32']
#spec.cc.include_paths += ["C:/Windows/system/include"]
spec.linker.library_paths += ["C:/Windows/system"]

`RUBY_PLATFORM` may not contain `mswin` or `mingw`; Add `msys`