Improve compiler single-file run syntax

spec/compiler/compiler_spec.cr

@@ -27,4 +27,15 @@ describe "Compiler" do
       end
     end
   end
+
+  it "treats all arguments post-filename as program arguments" do
+    with_tempfile "args_test" do |path|
+      `bin/crystal '#{compiler_datapath}/args_test' -Dother_flag -- bar '#{path}'`
+
+      File.read(path).should eq(<<-FILE)
+        ["-Dother_flag", "--", "bar"]
+        {other_flag: false}
+        FILE
+    end
+  end
 end

spec/compiler/data/args_test

@@ -0,0 +1,7 @@
+# Last argument is file path to write
+test_path = ARGV.pop
+File.open(test_path, "w") do |f|
+  ARGV.inspect(f)
+  f.puts
+  {other_flag: {{flag?(:other_flag)}}}.inspect(f)
+end

src/compiler/crystal/command.cr

@@ -462,6 +462,13 @@ class Crystal::Command
         filenames << stdin_filename
       end
 
+      if single_file
+        opts.before_each do |arg|
+          opts.stop if !arg.starts_with?('-') && arg.ends_with?(".cr")
+          opts.stop if File.file?(arg)
+        end
+      end
+
       opts.unknown_args do |before, after|
         opt_filenames = before
         opt_arguments = after