Merge pull request #2628 from fenrir-naru/cygwin_host

Under cygwin host, ncurses.a is only available instead of termcap.a.

mrbgems/mruby-bin-mirb/mrbgem.rake

@@ -6,8 +6,12 @@ MRuby::Gem::Specification.new('mruby-bin-mirb') do |spec|
   if spec.build.cc.search_header_path 'readline/readline.h'
     spec.cc.defines << "ENABLE_READLINE"
     if spec.build.cc.search_header_path 'termcap.h'
+      if MRUBY_BUILD_HOST_IS_CYGWIN then
+        spec.linker.libraries << 'ncurses'
+      else
         spec.linker.libraries << 'termcap'
       end
+    end
     spec.linker.libraries << 'readline'
   elsif spec.build.cc.search_header_path 'linenoise.h'
     spec.cc.defines << "ENABLE_LINENOISE"