rework Rakefile.rb to allow cross-compiling from cygwin

Rakefile.rb

@@ -12,11 +12,31 @@ base_env = Rscons::Environment.new do |env|
   env["CCFLAGS"] += ["-Wall", "-O2"]
   env["CFLAGS"] << "-std=gnu99"
   env["CXXFLAGS"] << "-std=gnu++11"
-  env.parse_flags!("!sdl2-config --cflags --libs")
-  env.parse_flags!("!freetype-config --cflags --libs")
-  env.parse_flags!("!pkg-config --cflags --libs ruby-1.9")
-  env["LIBS"] += ["dl"]
-  if RUBY_PLATFORM =~ /mingw/
+  if RUBY_PLATFORM =~ /cygwin/
+    env["CC"] = "i686-pc-mingw32-gcc"
+    env["CXX"] = "i686-pc-mingw32-g++"
+    ruby_location = ENV["RUBY_PATH"] || "/cygdrive/c/Ruby193"
+    sdl2_location = ENV["SDL2_PATH"] || "/cygdrive/c/apps/SDL2"
+    freetype_location = ENV["FREETYPE_PATH"] || "/cygdrive/c/apps/freetype"
+    env.parse_flags!(<<-EOF)
+      -I#{ruby_location}/include/ruby-1.9.1/i386-mingw32
+      -I#{ruby_location}/include/ruby-1.9.1
+      -L#{ruby_location}/lib
+      -Wl,--enable-auto-image-base,--enable-auto-import
+      -lmsvcrt-ruby191 -lshell32 -lws2_32 -limagehlp -lshlwapi
+
+      -I#{freetype_location}/include/freetype2
+      -L#{freetype_location}/lib -lfreetype
+
+      -I#{sdl2_location}/include -Dmain=SDL_main
+      -L#{sdl2_location}/i686-w64-mingw32/lib -lmingw32 -lSDL2main -lSDL2 -mwindows
+    EOF
+  else
+    env.parse_flags!("!pkg-config --cflags --libs ruby-1.9")
+    env.parse_flags!("!freetype-config --cflags --libs")
+    env.parse_flags!("!sdl2-config --cflags --libs")
+  end
+  if RUBY_PLATFORM =~ /mingw|cygwin/
     env["LIBS"] += ["opengl32"]
   else
     env["LIBS"] += ["GL"]