title: kotlin-native: missing SDL.h when building sample tetris app on Windows via MSYS2
body: <p>I have a 64 bit system with windows 7. I built kotlin-native via <code>gradlew dist distPlatformLibs</code> then entered a msys2 terminal and via pacman installed the mingw sdl2 lib. Via winpty I execute the Tetris sample app's <code>build.bat</code> and get the following compilation exception:</p>
  
  <pre><code>$ winpty ./build.bat
  Exception in thread "main" java.lang.Error: C:\Users\me\AppData\Local\Temp\tmp4397933690362265283.c:1:10: fatal error: 'SDL.h' file not found
          at org.jetbrains.kotlin.native.interop.indexer.UtilsKt.ensureNoCompileErrors(Utils.kt:137)
          at org.jetbrains.kotlin.native.interop.indexer.IndexerKt.indexDeclarations(Indexer.kt:902)
          at org.jetbrains.kotlin.native.interop.indexer.IndexerKt.buildNativeIndexImpl(Indexer.kt:892)
          at org.jetbrains.kotlin.native.interop.indexer.NativeIndexKt.buildNativeIndex(NativeIndex.kt:56)
          at org.jetbrains.kotlin.native.interop.gen.jvm.MainKt.processCLib(main.kt:284)
          at org.jetbrains.kotlin.native.interop.gen.jvm.MainKt.interop(main.kt:38)
          at org.jetbrains.kotlin.cli.utilities.InteropCompilerKt.invokeInterop(InteropCompiler.kt:97)
          at org.jetbrains.kotlin.cli.utilities.MainKt.main(main.kt:29)
  </code></pre>
  
  <p>Disabling <code>@echo off</code> in the script I can see the above exception happens during the call to <code>call cinterop -def ".\src\main\c_interop\sdl.def" -compilerOpts "-I\msys64\mingw64\include\SDL2" -target "mingw" -o sdl || exit /b</code></p>