Refactor Crystal::Scheduler#fatal_resume_error for win32

src/crystal/scheduler.cr

@@ -97,11 +97,23 @@ class Crystal::Scheduler
   end
 
   private def fatal_resume_error(fiber, message)
-    LibC.dprintf 2, "\nFATAL: #{message}: #{fiber}\n"
-    caller.each { |line| LibC.dprintf(2, "  from #{line}\n") }
+    print_error "\nFATAL: #{message}: #{fiber}\n"
+    {% unless flag?(:win32) %}
+      # FIXME: Enable when caller is supported on win32
+      caller.each { |line| print_error "  from #{line}\n" }
+    {% end %}
+
     exit 1
   end
 
+  private def print_error(message)
+    {% if flag?(:unix) %}
+      LibC.dprintf 2, message
+    {% elsif flag?(:win32) %}
+      LibC._write 2, message, message.bytesize
+    {% end %}
+  end
+
   protected def reschedule : Nil
     if runnable = @runnables.shift?
       runnable.resume