add spec for check_cfg with a :package argument

build_tests/configure/check_cfg_package.rb

@@ -0,0 +1,7 @@
+configure do
+  check_cfg package: "mypackage"
+end
+
+Rscons::Environment.new(echo: :command) do |env|
+  env.Program("myconfigtest", "simple.c")
+end