Fix rbx-1.2.4 setup phase

Rubinius back then didn't have a Gemfile, so don't try to invoke `bundle`.
Instead, rely on the host Ruby to already have rake installed.

bin/ruby-build

@@ -514,7 +514,7 @@ build_package_ree_installer() {
 build_package_rbx() {
   local package_name="$1"
 
-  { bundle --path=vendor/bundle
+  { [ ! -e "Gemfile" ] || bundle --path=vendor/bundle
     RUBYOPT="-rubygems $RUBYOPT" ./configure --prefix="$PREFIX_PATH" $RUBY_CONFIGURE_OPTS "${RUBY_CONFIGURE_OPTS_ARRAY[@]}"
     rake install
     fix_rbx_gem_binstubs "$PREFIX_PATH"

test/build.bats

@@ -459,7 +459,7 @@ print '>>'
 OUT
   cached_tarball "rubinius-2.0.0" bin/ruby
 
-  stub bundle '--version : echo 1' true
+  stub bundle false
   stub rake \
     '--version : echo 1' \
     "install : mkdir -p '$INSTALL_ROOT'; cp -fR . '$INSTALL_ROOT'"
@@ -469,7 +469,6 @@ install_package "rubinius-2.0.0" "http://releases.rubini.us/rubinius-2.0.0.tar.g
 DEF
   assert_success
 
-  unstub bundle
   unstub rake
 
   run ls "${INSTALL_ROOT}/bin"