add Rscons.glob - close #50

build_tests/library/override_arcmd.rb

@@ -1,4 +1,4 @@
 Rscons::Environment.new(echo: :command) do |env|
   env["ARCMD"] = %w[ar rcf ${_TARGET} ${_SOURCES}]
-  env.Library("lib.a", Dir["*.c"].sort)
+  env.Library("lib.a", Rscons.glob("*.c"))
 end